Our favorite teams are tied. Forget underlying Pythagorean reality. These two teams are equal. There are different ways to look at this which will enable both fanbases to be pleased with their teams' performances so far. At the very least, they can convince themselves that their teams will improve in the second half.
A Yanks fan could start out with this fact: Chien-Ming Wang has been worse than Steve Trout and yet(!) the Yanks have kept up with the Sox. A Sox fan could counter with Matsuzaka. Dice-K has also been worse than Steve Trout and yet(!) the Sox are tied with the mighty Yanks. Oh yeah, someone on the Bronx side would retort, well, if you told me the Yanks would be 0-9 against the Sox and still be tied at this point in the season, then I'd consider myself lucky. And another Sox fan might point out that the Sox are 9-0 against the Yanks. Then there would be silence. At this point, a Yanks fan could bring up A-Rod's early season injury. How are the Yanks tied with the Sox when for a whole month Cody Ransom played instead of Alex Rodriguez? That's a net loss of 10 games right there! The Yanks would be up 10 games right now if he played the whole season.
Ah, another Boston fan would return the serve, you forget Big Papi. Yeah, he's back now. But for two months, he was giving away games with his bat. How are the Sox tied for first after Big Papi stunk for those two months?
The Yanks have sub .500 record against really good teams and yet they're in first place!
The Red Sox have trouble against the not-so-great teams.
Joba has regressed.
You already said that!
And so both teams' fans would agree. New York and Boston are first place teams despite being pretty bad. They are sure to improve since they weren't living up to their potential before.