My sister in law has this phone and i just read that the official froyo update is available for the MyTouch 3G Slide. It fixes a lot of things on the phone and othe minor issues. I hope you enjoy. I know my Sister-in-Law will when my brother updates it for her. Froyo (Android 2.2) is some 500 times faster than 2.1 in some issues. Im glad you guys are getting it but isn't this pretty late? My EVO 4G is getting ready to get Gingerbread 2.3. Any update is a good update especially when it's a jump from 2.1 to 2.2.
Here is the link...
T-Mobile myTouch 3G Slide gets in with its Android 2.2 Froyo update - Phone Arena
HTC link...
HTC Mobile Phone Support - T-Mobile myTouch 3G Slide