Okay, a rather long title - but lets look at this objectively as possible from the perspective of someone who has been an Eagles fan for 30 years and spent all of that time living in Deadskin territory surrounded by Deadskins fans.
The front office better be right on Kolb - all of the pressure in the world is now on Kolb. If McNabb wasn't the best Eagles QB ever he was the best Eagles QB of the modern (post NFL/AFL merger so we will exclude the pre-merger Hall of Famers from consideration) period. Yes, I'd rank Randall Cunningham as my favorite Eagles player ever and I strongly advocate for Cunningham's induction into the NFL Hall of Fame, but McNabb was more accomplished and did it for longer. So Kolb has the pressure of having to replace a bona fide legend. While McNabb suffered from Andy Reid's strange adversion to calling running plays in later years and always suffered from bad to mediocre wideouts, McNabb has a very impressive record of winning. Blame him if you like for the Eagles not bringing home a Super Bowl (I don't), but without McNabb the Eagles would have never been in the position to disappoint us so many years.
Really, while the success of the second round pick may decide whether it was better for the Eagles to trade McNabb now or let his contract expire that is secondary to the question of whether Kolb is the guy. I've known since they drafted Kolb that Kolb would be the successor to McNabb and I believe that he will be good. Of course, if I am wrong that Kolb will be good, the second round pick is likely to be a footnote.
From the other side, it seems that Washington made a major mistake - Daniel Snyder repeats the same move over and over again - get a big name and then watch them disappear. While McNabb is an upgrade over Jason Campbell, Campell and the 2nd Round Pick may have been a better choice. My take is that getting McNabb would make sense for a team who might be a quarterback away from competiting for a playoff berth - but makes no sense for a team which has major needs and is in need of a major infusion of young talent. Washington is likely to be a bad team with either Campbell or McNabb as quarterback next year. With all of the holes in that team, it is likely that they will realize that McNabb was a bad pick up - while a young Donovan McNabb may have been able to win games by himself, McNabb does not appear to have that talent anymore. While Washington may be excited to get McNabb, it seems that even with a new coach and manager it is the same old Daniel Snyder as owner - Snyder has turned the Deadskins into the joke of the NFL by making moves like the McNabb move - a splashy on paper move that is likely to backfire. Getting McNabb only makes sense if you believe that you can win now or next year (assuming you resign him) - it makes no sense for a team that requires almost a complete rebuild.
My guess is that McNabb Deadskin jerseys will hit the bargain rack before Kolb Eagles jerseys do - while Kolb is being handed the keys to a young, talented offense, McNabb is getting the keys to an offense which is similar to the ones he had prior to Brian Westbrook. After 11 years with one coach, McNabb is put into a new system. Rather than young, talented offensive weapons, McNabb has a group of aging former stars and a tight end. In other words, Kolb is set up to be a success in Philadelphia while McNabb is set up to be a failure in Washington. If Kolb fails after two years, it will fall entirely onto his shoulders - the front office has provided him with every chance to suceed. If McNabb fails in Washington, he'll merely fulfill the realistic expections given what he had to work with.
McNabb deserves better than Washington - Washington doesn't deserve as good as McNabb.