Pheace: there's no better time to buy than on Steam Summer/Xmas sales.
Thats a bit misleading. What you have at Christmas/Summer Sales is daily deals(50-90% off) for relatively few titles, 33-50% off for the smaller indie like publisher catalogs(most smaller/indie publishers participate), and lame ass 20-33% discounts on participating big name publisher catalogs(apart from THQ, Square, and maybe some Ubisoft stuff, dont count on big discounts _if any_ that are not tied to daily deals QQ).
Meanwhile there are random 50-90% off daily/midweek/weekend sales all year long that can easily beat the 33% summer/winter sale discounts, if those particular games dont happen to be in the daily deals section.
So yeah, seasonal store wide sales are nice, but people tend to exaggerate their importance.