Oh, I don't hang out there - "there" meaning "the semiofficial buttcoin forums at bitcointalk.org". If my ability to suffer fools on CFC is so poor, imagine what it would be like there.
And yes, it is incredibly easy to calculate the RoI. You know, if buttcoins could be reliably exchanged for USD at a more or less constant rate. Which they can't. You could buy a buttcoin for twenty bucks, twenty cents, or twenty Gs. But even if you do use an expectation based on the recent average trend lines on the larger buttcoin markets, ignoring outliers, you still end up with the conclusion that buttcoin mining hasn't been even theoretically profitable for anybody except for maybe the first few months of buttcoins' existence.
And yet, people mine anyway. There are pages and pages of the SomethingAwful buttcoin threads devoted to pictures from bitcointalk.org of people and their mining rigs. Why do they do this? Because they are incredibly stupid. And that's why they're so easy and fun to mock.
Side note: I saw Skyfall in theaters back in November with a few friends. When the movie reached the part where Bond is interviewed by Silva in his computer room on the deserted island, one of my friends nudged me and joked, "I wonder how many buttcoins he's got in his wallet." When Silva's laptop was taken back to MI-6 for examination, I shot back, "Oops, I think Q just deleted the wallet file. So much for that world-domination scheme."
Judging from the outrageously over-the-top response, somebody's feeling as though those remarks hit a bit close to home. Let's ignore the probably-true-but-not-worth-arguing claim that right-libertarians usually come up with bad ideas and focus on some more amusing nuggets.
Your assertion that buttcoins have an "intentionally limited use" is hilariously off the mark. One of the primary reasons the buttcoin "community" is so relentlessly mocked is because many of these buttcoiners do this out of a conviction that, when the "unsustainable" global economy collapses, buttcoins will remain one of the only viable methods of exchange - making everybody who got in on the ground floor of the buttcoin phenomenon the potential world capitalist elite, transforming them from the stereotypical goons in their parents' basement into Randian superman captains of industry. They do not hold these opinions secretly. It's not to say they proselytize, because that would involve sharing their potential (a word I use extremely loosely) gains with others. (Given the finite amount of buttcoins and the nature by which later mining occurs, namely, more work to churn out smaller fractions of a buttcoin, anybody who got into buttcoin mining in the recent past, not to mention nowadays, is getting virtually nothing out of it anyway.) It's more that they brag about their prescience in any venue they like.
True, there are people who do not view buttcoins in this way. There are those who view buttcoins as a method for transferring sums of, uh, buttcoins without any possibility of oversight from anybody else. Rumors about criminal wetwork being paid for with buttcoins - "contract killers" seems to be a buzzword, as though there were all that many of those around - have persisted around the community nearly as long as it has existed.
There have been the efforts to set up buttcoin-mediated businesses, or to persuade extant businesses to accept buttcoins as a valid means of exchange. The latter have been almost wholly unsuccessful (I believe the only notable "success" was a New York restaurant that accepted buttcoins for a few months before deciding that the whole thing was stupid and not worth it); the former are slightly more interesting, because of their potential for actually working out. Most of them never do, though. For whatever reason, it's hard to find a good or service whose provider and consumer both possess and want buttcoins. Nevertheless, some brave souls have soldiered on, and, you know, that's cool, running a legitimate business with a medium of exchange that nobody else wants. It's not hurting anybody and it's almost kind of neat. If these were the main examples of buttcoiners, then you'd be right: there really wouldn't be much to laugh about.
The problem is that these legitimate businesses are (small and scattered) islands in a sea of dung. Far more common are the efforts to set up a business without actually figuring out how businesses work (ah, the mark of the Randian superman) and rejecting the advice of those who do know how they work and who, out of pity or whatever, have tried to help. (There was one notable case of a person who wanted to operate a porn paysite on buttcoins, but who continually rejected the halfhearted advice of a proprietor of an actual porn paysite on the grounds that, lol, what does she know?)
Or, alternatively, the efforts to defraud other people of their buttcoins. There have been more major buttcoin fraud scandals in the past few years than can be counted on two hands, and innumerable minor ones. This is especially easy because buttcoins are basically untraceable: one of their cryptographic appeals. What makes them an interesting experiment in computation makes them ideal for the fraudster who wants to just take the "money" and run: it's virtually impossible to prove who possessed what and when to any reasonable degree of confidence, so any effort to employ legal action to recover these "monies" would be laughed out of court. Sometimes these frauds have involved buttcoin amounts equivalent to hundreds of thousands of American dollars, according to the then-current exchange rates on the largest buttcoin market (although in reality, who the hell even knows, because there's no central buttcoin regulatory organization). That such relatively large sums of cash-equivalents were involved might be considered to be something of a feather in the buttcoiners' collective cap if, you know, we weren't talking about unprosecutable fraud. (Or about how amusing it is that buttcoiners who claim that their little project is the wave of the future and that the US dollar is inflating itself to nothingness still measure the "success" of their project by dollar-equivalents.) Hilariously, this has led to calls by some of the more easily duped buttcoiners for some sort of independent group to monitor, warn about, and prevent fraud. Which kinda sounds like a government type thing. Just a little bit. And there's not the tiniest hint of irony in antigovernment libertarian heroes clamoring for the institution of some kind of independent oversight because they can't trust each other not to defraud everybody else. No sir.
I mean, any neutral observer could easily see how much of a target these fruits make themselves. It could've been a fairly interesting math/CS experiment, but then the libertarians got ahold of it. And then it could've been a slightly less interesting but still somewhat interesting example of a niche medium of exchange, but then they started making outrageous and grandiose predictions, doing insanely stupid stuff to try to mine buttcoins, and defrauding everybody in sight. It's hard to pity them, because so many of them are gleefully either complicit in their own fates or, alternatively, attempting to do the exact same thing to other people. And frankly, everybody else who's been trying to use buttcoins for something legitimate should've seen where this whole thing was going and lit out for the territories a long time ago.
Pure gold! I wish Cathy would post more 
Memento
