I am moderately strict with them, I guess.
For the other half of the question, there are a fair few of them among PCs, NPCs and monsters. Not tons, but yeah, a fair few. And when I'm player-side, I tend to favour not taking them, or taking only one per PC.
I take a 'default-deny' stance on PrC's, feats, and all other *optional* (i.e., usable at the GM's discretion, as all PrC's explicitly are even in straight D&D, for example) components though. A lot don't get through the filter. But then, that's probably just as well, because I'm (usually) drawing from substantial numbers of WotC, 3rd-party, internet-derived and my own sources for them.