Muhlenberg College/Allentown Morning Call. Likely Democratic primary voters. MoE 5%
4/28 - 5/1: Specter +6 (48/42)
4/29 - 5/2: Specter +9 (49/40)
4/30 - 5/3: Specter +4 (46/42)
5/1 - 5/4: Specter +8 (48/40)
5/2 - 5/5: Specter +5 (45/40)
5/3 - 5/6: Tied (43/43)
Yesterday, Sestak launched his campaign's make-or-break ad, going after Specter for his party switch. That ad may have had some impact on these numbers because 1/4 of the poll was conducted yesterday. However, these numbers do seem to have been bouncing around a bit, and they do include the results from 5/3, which was a good day for Sestak.
Within the next week or so, we should know whether Sestak's new ad is working. At this point, however, it seems pretty clear that this race is far from over, and it would certainly be a mistake to count out Joe Sestak.
Update (2:20PM): Next week we'll be going into the field with a Pennsylvania Democratic primary poll. Should be very interesting results!