Bring up Launcher Pro in your Settings > Applications menu, then click the "Clear Defaults" option. The next time you hit Home, it will ask you which you want to you, and give you the option to set that choice as your default.
Mine started doing that, and it seems that it was related to one of the Widgets I had running - I got rid of all my widgets and it suddenly stopped. I've been adding them back one at a time to try to locate which one (if any). Might be something different for you, but just a thought.
Verizon: Took my DInc into the store because it was randomly shutting down (Froyo update seems to have fixed it), the rep couldn't figure out what was wrong, so installed a task killer - claiming it may be resetting because it was running out of available memory.
Be aware, however, that the 2GB cap is separate from your 5GB data cap. If I understand it right, You pay $20 extra for an additional 2GB reserved for your tethering.
I could be wrong, but that's how it was explained to me.