The number one, primo, super-duper, first, most annoying issue Tablet users will find with Vista Beta 1 is: lack of driver support.
Vista is undergoing a lot of changes under the hood, and this means that a lot of device drivers will have to be rewritten or updated to work under Vista. This is not unheard of in the history of Windows OS development, so you should not be surprised.
Backwards compatibility is not completely lost though, as you can force your existing XP drivers onto a Vista system and they'll work in most cases. If your driver is an EXE, you can go to its properties, the Compatibility tab and check "Run this program in compatibility mode for:". Then select an OS that you want your EXE to think it's running in. Most of the time, Tablet users will want Windows XP. If you find a mainstream use for Tablets to run apps in Windows 95 or WinNT4 SP5 emulation, let me know :P
The most common driver types that I've encountered that need babying are:
So if you really have to have Vista Beta 1 on your Tablet, be aware of these issues, put your XP drivers on a USB flash drive, and cross your fingers!
(updated 8/2/05: fixed title for consistency with my other Vista Beta 1 posts)