It's been very plot-dependent
So has how fast does it take for a vampire to rise. That rather annoyed me.

Silly addictions...you know really, outside of Cordy and her wardrobe (ditto BUffy) did anyone have silly little addictions? I mean it's not like Willow collected frog figurines or Faith had the largest Santa collection in SW California or anything really that normal people might do. Hmm, Giles had an addiction to vinyl records...