Clicks go up on weekends because different purchasers feel they get more direct traffic from visitors on the weekends. For instance click buyer one may have a high click of $7 set on their keywords but click buyer two is not bidding higher than a $1 so buyer number one always has the high bid at say $1.10. On the weekend number two decides to raise his bid to $4 which brings number one to $4.50 a click automatically or puts them in second place.