One big question is how long developers will take to make some quality third-party software available for the Palm Pre. Although Palm is talking to developers about its planned application development framework for WebOS, it hasn't actually given them a working SDK just yet.
Some current Palm Treo users might also care about backward compatibility with existing PalmOS applications. That group isn't nearly as big as it used to be, and it's getting smaller every day; as a result, Palm will apparently leave it to third-party software developers to create emulators and other tools that would enable old PalmOS software to run on WebOS.
Also, with the Palm Pre itching to get out of the gate, Google already on the march with Android, and Apple's iPhone simply running amok, Microsoft will have a much harder time getting anyone to care about Windows Mobile, which still sports a UI that looks like it kissed the business end of an ugly stick.
For more details about the Palm Pre and WebOS, including some screenshots of the Pre in action, check out this article over at Linuxdevices.com. You can also check out InformationWeek's coverage of the Palm Pre's CES debut here and here.