I'm really of many, many minds over the Favre trade to the Jets. First of all, I think the Pack did the right thing. You can't plan your future around a dude who's yo-yoing you around. I think, for the Jets, this deal has impressive upside and tremendous, tremendous downside. Favre won't take them to the Super Bowl. But he might take them to the AFC championship--where he will promptly throw a 4th quarter pick.

For me, the most interesting part of this deal isn't Brett Favre, but Chad Pennington. There is exactly one way that the Brett Favre trade could go bad for Green Bay--if Pennington gets traded, or picked up by, the Vikings. That will be a disaster for Green Bay, because the Vikings--with Pennington--will likely stomp a mudhole in that division, and much of the NFC (Cowboys included). Here is my case for Pennington, courtesy of CHFF:

...he boasts the 7th best passer rating in NFL history (88.89) and the No. 5 mark among active players. Believe it or not, Pennington had a better career passer rating than Tom Brady heading into the 2007 season.
Pennington is also the most accurate passer in league history, with a record 65.61 career completion percentage. Hard to believe, considering he puts up so many parabolas that the networks want to hire him as a sideline sound man following his next rotator cuff injury in October.
And the lack of a laser, rocket arm is compounded by the quality of the offensive talent around him, which has never been spectacular.
But proof of Pennington's proficiency is evidenced by the fortunes of the Jets when he plays and when he doesn't: Pennington has played in 12 or more games just three times in a season since replacing Vinny Testaverde in 2002. The Jets have made the playoffs all three of those seasons (2002, 2004, 2006). They failed to win even half their games every other season (2003, 2005, 2007).
Head coach Eric Mangini was "Man-Genius" in his rookie season at the helm in 2006. Pennington, not so coincidentally, played every single game for the one and only time in his career that year. Mangini became a duplicitous rat turncoat in 2007 while his team struggled through a 4-12 sophomore campaign - and Pennington started just 8 games.

Of course all of that rests on Pennington not getting hurt. Yeah, that's a big qualifier hanging out there.