Small spec bumps in the Spring are pretty normal, but Apple also seems to be changing their product cycles around. I wouldn't expect any big changes until October, and I wouldn't expect any spec bumps at this point to be a direct part of WWDC, maybe something around that timeframe but WWDC itself will be focused on SL and iPhone 3.0, and maybe the 2009 iPhone.
It does seem likely that the 2.0Ghz Aluminum will get a processor bump, doesn't seem right for the White model to have a newer faster processor revision for very long. I would see that as the biggest reason to wait a bit.