I've been running Windows Mobile 6.1 on my T-Mobile Dash for a little over a week now. Thus far I'd have to say I'm pretty happy with it. I downloaded the ROM from xda-developers.com, and the process to set it up was very straightforward. The only thing I haven't been able to find yet is a birthday plugin for the new home screen.
Instructions for the upgrade are here. Note that this upgrade is not supported by T-Mobile, so if it goes wrong, you're on your own. Enjoy!
Posted using Stirling Blog on Windows Mobile