There’s an official whitepaper available now if you’re looking to use Windows Mobile 6 devices with Small Business Server 2003.
Not a whole lot of changes from the previous doc for WM5 devices.
Main thing to remember is that WM6 only works with certain minimum versions of ActiveSync (4.5) and Windows Mobile Device Center (6.1). And, of course you have to keep straight which of those sync options works on XP and which works on Vista. Which you should already know by now, honestly.
Nice section on certificates, with decent coverage on the now-preferred method of using a 3rd party certificate, rather than SBS’ much-loved-until-WM5–came-out self-signed cert.
The troubleshooting section is worth a look too. Especially if you’ve ever been ready to pull your own hair out while trying to troubleshoot synchronization problems with Windows Mobile devices.