-all things being equal how does volume of searching on Saturday compare to M-F? how about Sunday?
That depends on your sector. Being in b2b I see that volume of clicks start dropping on a Friday afternoon (GMT). Figures continue to plummet as the weekend goes on (thus Sunday is worse than Saturday).
By the end of Monday though, stats reach their peak once more and this plateau's through until POETS day comes around again.
As far as I'm concerned my target audience probably only works 4 1/2 days a week at best...;-)
Syzygy
You need to measure your traffic patterns over both the short term (a week) and the long term (month/year) as often b2b traffic (depending on your product) has higher traffic in the first or last week of a month as well.