Better screen, more powerful processor, improved keyboard, more powerful speakers etc.

The bold will also come with the latest blackberry os available. Allowing video recording, 16gb microsd cards html email and more. Other devices might be upgraded later but when that will actually happen and how well they will run is an open question.

It is possible to upgrade the OS on windows mobile devices. Check out the forums at ppcgeek.com or xda-developers.com. Those guys keep on top of every new os release.