The reason why PHONAK handed over the jersey easily was because Landis knew that his team is not as strong and he didn't want his boys to defend the jersey with 3 hard days in the Alps still to come. With the jersey in Pereiro's shoulders, it will be his teams' responsibility to control the attacks.
The only problem is that Pereiro is not your average Joe Rider. He placed 19th last year and placed 2nd in the most difficult stage. And there is this notion that the yellow jersey gives the wearer the strength of two men! And that's one of the arguments that says that Landis was wrong in giving up the jersey.
But in the end, I think Pereiro and his team isn't strong enough to take the jersey to Paris. If I were PHONAK, I'd rather keep an eye on Dennis Menchov and RABOBANK and its possible collusion with DISCOVERY CHANNEL. Cadel Evans has a good chance of making it to the podium but with a team halved between helping him and Robbie McEwen for the green jersey, he's a long shot of wearing yellow.
The fight for the yellow jersey is realistically between Landis, Menchov and Evans. But nothing is set in cement here. The Alps will help to weed out the weak and the sick while putting the true king on is throne.
An example would be Liquigas rider Magnus Backstedt who is 6"6' and 200lbs (Lance Armstrong was 5"10' and 158lbs). Because of his size, Backstedt produces so much power that the possibility of his bike breaking apart during racing conditions is always an issue. So BIANCHI made a custom made titanium frameset for "Maggie" instead of a carbon fiber steed.