I think Apple would be silly to release another MAJOR product at WWDC. In the short term it would take the limelight off the iPhone SDK, iPhone 2.0, 3G iPhone etc.
Not to mention that for the first time as a Mac user (and I mean Macbook, OS X), I feel rather neglected. My Macbook is great, apart from the heat, constant fannage, electrical whine (which comes through on my sound recordings even through an external sound card), ongoing battery problems. blah blah... Leopard is a mess too. Many, many bugs, for me at least.
It just seems as though a snazzy new product would be great for the media spin and share price (perhaps). But what about consolidation/evolution, sorting out leopard, releasing newly designed macbooks that are much more solid machines. I have an iPhone, and I'm really excited to see the next one.. but again, consolidation and evolution would be nice. But to add a whole new major product?! Maybe in a year or two, but I hope not now!
That said, maybe they have done something clever with Multitouch - fingerworks style tablet accessory maybe. Or maybe there's a new software thing (more WWDC relevant). I haven't thought about it too much. I just hope this 'new' thing isn't too ambitious!