Always nice to see objectivity go out the windown in the midst of a intra-division rivalry.
Vikings fans are delusional if they think that Favre isn't a dramatic improvement over Jackson in 2008. Before you react - stop and reread the last sentence. I said "in 2008." Even the most passionate TJ supporter has to acknowledge that he's a developmental QB prospect with absolutely no guarantees as to where he'll end up, or even that he'll keep improving.
Frankly, I think TJ's ceiling is somewhere around Gus Frerotte's (a guy on your roster too, coincidentally enough) who can spot start for teams and win games, but who you don't want as your starter long term. And for now, I'd probably trust Frerotte as my starter more than TJ just because I can rely upon a veteran to avoid mistakes more than a young QB.
Regardless, outside of the QB position, the Vikings are in the top 10 of teams with the most talent, and playing in the weaker conference have a great opportunity to make a strong playoff run. Choosing to force the rest of the team to wait while you develop Jackson, instead of acquiring a guy like Favre, is insanity under the circumstances.
Obviously, the cost for acquiring Favre needs to be acceptable, but that's a separate issue. I'm just addressing the notion that TJ is good enough that you don't need Favre.