I hadn't finished all of Quake without cheats until 2 years ago, and even then only on Normal.
I don't like Quake 2 and have never finished it. Though I did finish Quake IV for some reason (mainly 'cos it was easier, I think) I'd pay stupid amounts of cash for a new Quake "universe" SP game
My lack of enthusiasm for MP is mainly due to my lack of skill at it (more than my story-telling pretence)
Due to having so many extended breaks from modding, I basically have to relearn everything from scratch. (Obvious, I know #1) - this is particularly problematic when restarting a mod - I know I'll struggle to get to grips with the Gate/"Horde" type code in eQ if/when I ever get back to it.
I still have pretty much no idea how the fundamentals of QuakeC work (Obvious, I know #2)
I never use the grid or any numbers for working out geometry when mapping. It's all by "eye". (Obvious, I know #3)
I'm always reluctant to release qc code or .maps for mods due to how crappy they are.
The only reason eQ uses Quake monsters is because I can't model new characters to use.