According to crave:

Over a seafood dinner with HP management last Friday, the PC maker offered more than just aorta-clogging cuisine. In an informal chit-chat session, we learned that HP is readying its first UMPC which may hit the market in late spring.

While I can't make any comments about which platform HP would be using for a UMPC, I can certainly say they would be a welcome addition to the UMPC market. For a big player like this to step into the ring is a great sign that the UMPC market is quite healthy. Any guesses on what type of UMPC they'll be putting out? Will it be a mini-note ala CloudBook / eee PC or will it be a slider like the OQO or Sony UMPC? It looks like Steve Paine is hoping for a slider. Me? I'm hoping for a super thin 9" mini-note with HSDPA built-in.