Most of my leagues drafted Pennington, Portis, and Driver in the preseason-draft, so they were not available on the waiver wire.
I just don't believe in any of my leagues, you would have been able to pick up free agents in one week, that would have beat 8 of the teams, but that was last year!
I do believe you need to watch the wire, and make good acquisitions throughout the year. Most of my leagues are not first come, first served in Free Agency however, so the worst teams get the first cracks at the free agent of the week. Thus, it is not always easy to get a great free agent, if your team is doing quite well.