I have about 815 hours. When I reached 700 I did the math and realized that worked out to about 30 solid days of gaming, that was last November, about a year after the games release. Some of those hours are time when I've fallen asleep for a few hours while playing and the game was on in the back ground, but still...
I cut back on playing as much as I could after I realized this. I've now cut back my play time a considerable amount, considering since November I've only added about 115 hours to the tally. I love the stats steam gives, there were times it would tell me stuff like 'you've played 90 hours of Civ 5 in the last 2 weeks' That's almost as much time as I spend on my job in 2 weeks! I like commenting and reading this forum now because its almost like therapy or something, to be able to talk about and think about something I like to do so much, without actually doing it.
I don't think there is much wrong with this kind of playing though as long as you can still balance it with regular life. There is a lot of worse things in the world people can be doing than playing a video game. It helps financially because when I'm spending this much of my free time doing 1 thing there is little time to spend money on other stuff. Also, I find to a small degree that it helps me with math skills; I'm not entirely sure why, but if I've been playing a bit of civ 5 in a week I usually find I'm better at basic math, I don't know if this is just me though but I've definitely noted the improvements. It even has other educational benefits, like learning the names of leaders and wonders etc. I've googled all the leaders and wonders in the game and wouldn't have if I wasn't into it.