Our T-Mobile tipster just sent us a bit of good news for current Dash users. It seems T-Mobile is going to be releasing Windows Mobile 6 as an upgrade for subscribers this spring. No exact date as of yet, but it seems like it's coming some time in the next few months. For free.
We're still looking into whether other phones can be upgraded to WM6, so check back to see if yours can. Most of the OS improvements aren't hardware reliant, so most should be fine.