A number of people mention this one way or another, but an explicit search for "local maximum" doesn't match any specific comment - so I wanted to throw it out here.

Wireheading is very likely to put oneself in a local maximum of bliss. Though a wirehead may not care or even ponder about whether or not there exist greater maxima, it's a consideration that I'd take into account prior to wiring up.

Unless one is omniscient, the act of a permanent (-ish) state of wireheading means foregoing the possibility of discovering a greater point of wireheaded happiness.

I guess the very definition of wireheadedness bakes in the notion that you wouldn't care about that anymore - good for those taking the plunge and hooking up I suppose. Personally, the universe would have to throw me an above average amount of negative derivates before I'd say enough is enough, screw potential for higher maxima, I'll take this one...