I find that my tube amp sounds best on the 365th day it's continuously left on; on the 366th day, however, it goes back to sounding like cr*p.
Do you leave your components on 24/7?
Lately I've been leaving my components on all the time, on the assumption that a) they'll be ready when I want to listen, and b) the on/off cycle ages the equipment (tubes, anyway) faster than leaving everything on. Is the latter a reasonable assumption?