I'm biased but I think they'll take a bit to find their groove. I don't want to underestimate them because an Eagles team at home against a division rival is dangerous. But you got McNabb that just doesn't look 100% yet, Shawn Andrews is hurting, Dawkins supposedly had some kinda injury, that may be slowing him down, Kevin Curtis has got to adapt to his new role, Lito Sheppard is out for a month, they got a bunch of guys in the LBs corps that (besides Spikes) are young and probably still adjusting to the game and not to mention, Spikes has to adjust to the Philly scheme. LJ Smith is still recovering from whatever hurt him in training camp. Ried has got a plathera of problems on his plate too.
So, I think it's going to take about half a season before they kinda get going and it might be too late by then (people forget just how injury prone Westbrook is and McNabb isn't likely to make it much longer). But I definitely think, provided the team stays relatively healthy for the season, they'll be much more dangerous the second half then they will the first.