I'm only semi involved in character creation, usually the extent of my intervention is selecting "volunteers" to play the Cleric and the Wizard. The cleric is necessary because I love a combat heavy session (I've mentioned previously: It is my best trait as DM). I find Wiz characters near indispensable for the kind of game I run (for some reason I can't fathom, I'm not thief friendly, got nothing against them).But the area I can be most intrusive in is: Character Names!
The players pick in this is very important to me. Silly names are right out! Usually overly complex, long or hard to pronounce will drive me into a frenzy.
I've really softened on this over the years, My new player a couple of days ago broke just about all my rules except silly. I did what I did now and gave him a short nickname and enforced it. He is Brew now( it was part of his incomprehensible name). Only thing I go active on these days is silly.
Really not sure why this is so important to me. It's not like I've had a ton of problems with this over the years.
I guess everybody has their quirks and this is a big one of mine.