Saturdays and Sundays are basically like weekdays to me in which normally I don't log on until 8-8:30ish pm EST. Unless I'm working night shift on rare occasions then I can generally make raids or help out any night of the week from 9pm-12am NP.
Tough to commit to anything on the weekends. Generally though if it is posted in advance that we are raiding (here and in motd) then I can plan my play time accordingly.
I like an announced target for a couple of reasons:
I think its the right thing to do.
Allows me to do some research on the mob.
Maybe I am just tired of hitting X mob and so I will take the party invite I wasnt that excited about.