I wouldn't say Tim Couch "never had it". He wasn't awful, he just wasn't spectacular. His QB rating, yards per attempt, all solid. His biggest problem was health, really. Missed more than half the year in 2000, then was hurt at the beginning of last year when Kelly Holcomb dazzled and instilled doubt in the minds of fans, coaches and teammates. He never really got a fair shake.
Plus, he had absolutely no running game. He had Terry Kirby in '99(who ran for a whopping 452 yards), then rookies the next 3 years(Travis Prentice, James Jackson and William Green), none of whom had particularly stellar seasons(Prentince-512 yards, 3.0 ypc, Jackson-554 yards, 2.8 ypc, Green-887 yards, 3.7 ypc).
The reason I'd think San Francisco would be a better stop than Green Bay is simply because Tim Couch is going to be 27 in July, and who knows how long Brett Favre has left. He's not the same quarterback he was 8 years ago, but if he wanted to play another 3-4 years, I bet he could. Green Bay picks 25th in the draft, anyway, meaning that Tulane's J.P Losman could fall right in their lap. San Fran picks 16th and has a chance to get one of the big time receivers, which would give Couch something to work with.