Yes, Arlen Specter's ahead RIGHT NOW. The election is in May and November is an eternity away in politics. And I agree with Frameshift's spot on comment about the idea of Specter "surging".
Comparing the polls should lead us to add a caveat; Arlen Specter vs undecided varies hugely depending on whose polls you cite. Franklin and Marshall have a lot of undecideds(50-44%). Daily Kos and Quinnipiac have fewer but it's still a decent number. DK's recent poll has 17% undecideds.
What all this suggests is that some of the support for Arlen Specter is 'soft'. If you look at all the polls you will notice that Quinnipiac and DK appear to be pushing their undecided with Questions like "Are you leaning towards one of the candidates?". Franklin and Marshall doesn't appear to be (judging from their much larger group of undecideds).
Voters who are asked this question think "I know who Arlen Specter is, better to go with the devil you know." They say "Specter" because they're lukewarm but have no idea who Joe Sestak is in Pittsburgh or Central PA. I've volunteered at Joe Sestak's campaign office a couple of times and yes, it's a little frustrating that Joe Sestak isn't closer; but Joe's one of 8 kids. People from big families learn to be fiscally conservative and Joe wasn't going to blow 2 or 3 of his 5 million on February advertising for a May election. Sestak's had plenty of appearances around the state and those might lead to a significantly larger sample (say 3000 Democrats or more) showing his small bump in name recognition that some of our phone bankers have seen. If Joe uses the remaining time to get his name out there in a way that's more efficient than 20-40 people American Legion Hall appearances, the polls could change quite a bit. Try polling in April after Joe airs his ads, and if it hasn't changed enough than you can say the race is over. But don't call it over just yet.