I've heard of other's revenue being down on weekends and this is certainly the case for me also. I think it comes down to traffic and your niche. You'd find that sites targetted towards the teens will actually see their revenue increase as the weekend is their time to be on the computer as long as they wish. Just my 2c... Ponynugget
My stats for today have dropped by about 30%, for some reason I find Tuesdays are always my best day of the week....
I have found that each of my sites have different on/off days.. for Zeropaid it's bigger on the weekends, but I figure thats because I don't get very many older people that have 9-5's. For my poker forum traffic seems pretty flat on weekends and bigger during the week. On Babe Galleria traffic stays even all week. Guess people like looking at hot chicks no matter what day it is lol.
Everything is better during the week because people are surfing from work.. Then on the weekends, they're out enjoying their lives, mowing the lawn, etc..