I wrote a couple weeks ago that I was done with Windows Mobile until Windows Phone 7 was released, in large part due to my sheer frustrations with the T-Mobile HTC HD2 performance. I just read and followed a link from an HTC Tweet that leads to a software update for the T-Mobile HD2. I actually sold my HD2 last week so I cannot test this out and am a bit sorry I did not wait longer to try this on the device.
I haven't yet found the official changelog, but from what I can find from sites like WMExperts the update includes an updated radio (hopefully fixing some of the connection issues), updated Swype (it was unusable on the HD2 before), and stability and responsiveness fixes (all things I had trouble with). So, if all of this is true then the HD2 may now be the device I had wanted when I purchased it. I am a bit disappointed that T-Mobile did not come out on their forums and say an update was coming out thanks to all the issues that people had been reporting.