IMHO, the quality and bugginess lotteries are rather good reasons to not pre-order. Bugginess and poor quality might get fixed over time, or might not. Or you may get lucky and get a fully functional quality game on release! (Like DX:HR seemed to be, for the most part, if you didn't mind the stuff about your character grabbing the idiot ball and walking out to get ambushed whenever it was time for a boss fight - not that that was ever fixed in a patch or anything anyways)
Examples of things that were or would have been mistakes to pre-order: Skyrim (PC version was buggy and crashy on release and the plot was so very dull - it got better but I could have waited and bought it cheaper), Spore (shallow but not buggy), Master of Orion 3 (basically complete shit on release, and still complete shit when the last patch came), Sword of the Stars II (incomplete, buggy, slow, but still better than moo 3 - got a few patches, one expansion, and then no more, leaving it incomplete and still buggy because the publisher (Paradox) wouldn't pay for any more, and Kerberos wouldn't, or couldn't, pay for more out of their own pocket, I guess).
At least if you're pre-ordering something like CoD you know what you're getting - they're that reliable, year after year, putting out a functional and reasonably fun game every time (if you aren't bored by the whole thing already).
If you're pre-ordering digital copies, if you're lucky valve will give you tf2 items (that are hopefully worth something if you don't play tf2) - the DX:HR ones were, anyways. Of course it'd have been far cheaper to just wait until it inevitably dropped to $5 rather than to pre-order it and then try to make some of it back by selling some of the tf2 items...