Yeah, what I would say is instead of concentrating on a certain number just try to be as efficient as possible when you model. Polycounts change so much between projects and advancements in hardware. This won't be a problem for you if you are an efficient modeler able to adapt.
If you go poking around in a next-gen computer game and take a look at the art assets carefully, either in-game (no-clipping to get really close is a good idea, or using sniper rifle zooms, etc :-), or in the editor, is a good idea to get a good idea of polycounts.
My answer would be, "as much as you need to reach the desired level of detail". I totally agree with Flewda. My experience is, that LODs are the key. The object can be insanely detailed from the close distance if needed. But over distance the polycount and especially the amount of material-IDs need to be reasonable.
^-- I vote that be the standard answer to any further such questions. Cody, if you don't know the answer to that question (or rather "how long is a piece of string") the answer is something like as long as it needs to be long enough etc. The polycount of any given item varies with what engine its going into, what end…