If GM Ted Thompson has structured the two-year contract extension the Green Bay Packers just gave to WR Donald Driver like he's done with other veterans in recent years, it's likely that it has few guaranteed dollars, but does raise his base salary to make sure he's paid like a starting receiver.
There are few (any?) 35 year old receivers who still play like Driver does, so it's hard to find similarities. But with big contracts recently handed out to Texans WR Andre Johnson and Dolphins WR Brandon Marshall, the ceiling for an NFL receiver's contract has certainly gone up.