We've been hearing from various delighted developers this weekend responding to Apple's redesigned provisioning portal. And yes, you can now delete many (not all) App IDs from the portal.
The newer the ID, the more likely it seems to be that you'll be able to select it, configure its settings and click that all-too-welcome delete button.
Did it work for you? Drop a note in the comments. Me? I've been happily weeding many apps out this weekend.