I agree with Foster. It's hard to just switch teams and it'll hit your credibility. I'd stick with the Vikes. And that's not because I don't want you here.
In the end, it's not Favre's team, it's a team that as Favre on its roster. I know that this one goes deeper than just some regular player, but dp you really want to abandon the Vikings organization over this? The franchise you love and rooted for for so long. Even if you want to put an asterik next to your SB victory, play-off run or wherever you're going, I think it'd be worth it.
If, after all that, you still think that you want to switch teams, go ahead. I think you'll be welcomed here by a lot of people, regardless of what team you'll pick.
To answer your question....
I do not feel too happy about what Favre did. We traded him, he's free to do what he wants, but the way he wiggled himself out of that Jets contract to get to the Vikings annoys me. Especially as a Packers fan.
I don't know how I'll feel if the Vikes win a Super Bowl. I don't feel that having Favre on that team will make it more sour or anything, though.
I don't like what he's done, but I will most likely forget about all the retirement sagas, late team switching etc. later on. I'm not angry about it, but it does pain you a little. I'm now still at the point that a punter wearing nr. 4 would sound like a pretty funny thing to do, though.