I haven't created a 'garbage' city to exploit the pop-rushing capability, so I have to extend Jove's question just a bit further to understand the exploit.
In release 1.29f, each pop-rushed citizen is worth 20 production points, but you can only convert 1/2 or less of your city's population into production. You can add a worker to a garbage city, and pop-rush a 20 point unit (perhaps an archer or spearman) on that turn (2 pop point converted to 1 pop and the unit.) Or, you can wait until you're 20 production short of what you're building, and then pop-rush the 1 worker to complete the build.
To get 40 production points out of a 'garbage' city, you'd have to add 3 workers (increase pop from 1 to 4), convert 2 to production (say a longbowman; pop goes from 4 to 2.) The two remaining pop points will be unhappy, so they are maintained as specialists. On the next turn the extra point will get starved out (there's no extra food in the city, and no way to build it up with only specialists.) So, if I've described this properly, the 40 production pop-rushing costs 3 workers (originally 30 production and 3 pop points), and requires a city reduced to 'garbage' status and the continued use of Despotism or Communism to allow the pop-rushing.
If I'm missing something, please enlighten me. If I'm describing things correctly, the use of excessive worker pop-rushing has limited utility.
Alright ... I've been thinking a little more about this. If two workers were added to the city (pop goes from 1 to 3), then production were set to spearman and production hurried (pop goes from 3 to 2, spearman set to be built), then production changed to longbowman and production hurried again (pop goes from 2 to 1, longbowman set to be built), this would maximize the worker pop-rush strategy (ideally 2x production vs worker cost). This technique could be extended to produce anything, as long as you had the right production cost intermediates to bridge up to the production cost of your intended item. I'm assuming that Civ3 allows the scheduled production to be changed once pop-rushing has occured (I don't know, as I haven't tried this.)
I think worker pop-rushing has its place. I hope I'm understanding the issue properly. And, again, if it remains disallowed, that's fine by me.