I think Chelsea will struggle a bit with width. Duff is a fantastic winger, but unless you play Robbin (sp?) on the right, there's no balance there. Geremi just isn't good enough. And even if you do, there's no cover for the wings - Duff is injury-prone. That said, the rest of that team is excellent, and they have to be favourites.
Arsenal were lucky to get away with poor squad depth last year. Campbell is usually missed frequently due to injury and/or suspension. Toure had an excellent season in central defense, but he may not necessarilly repeat that form. Pires is ageing, and I can't see him maintaining top form for long spells of the season, likewise Bergkamp. If they lose Vieira, they'll struggle to finish third. Otherwise, they'll be there or thereabout, but they won't win the title.
Man Utd look like a proper team for the first time in ages. They'll struggle initially with Ronaldo and van Nistelrooy out, but they finally have a strike force, rather than just a striker, and they have Ferdinand and Heinze coming in after a bit too. If they're close to the top at Christmas, I'm putting money on them.
Liverpool may improve, but short of Arsenal collapsing, they'll fall short. They don't have a pacy partner for Hyypia, so they'll struggle defensively unless they play Hamann. But if they play him and Gerard, they'll struggle to be creative enough. With the sale of Murphy (a huge mistake IMO) they have a grand total of two wingers (Kewell and Smicer), both injured, Smicer for a long time.
Newcastle have bought well, and I think they'll improve a lot this year. They finally have a holding mid in Butt, and a partner for Shearer in Kluivert. If Given, Kluivert and Robert all perform well over the season, Newcastle will be a bloody good team.