Never crossed upon any general-purpose stuff for GreaseMonkey - the only 3rd-party site modification I use is F.B. Purity, which has probably gotten too big to be a GM/TM userscript.
I do use it for a few things of my own - like color-coding specific elements on some websites, folding out really stupid clientside pagination elsewhere, and I'm considering to do some fixups for the time-registration software we use at work. A coworker and I already did a CSS override that fixes some problems, but it's hard to maintain (the stupid system has too many html element changes on upgrades) and would probably be easier to handle with GM user script.
