Turns out you have to uninstall Enterprise Library >= 3.0 before uninstalling the GAX/GAT. Did that and was able to uninstall.
I found that there is now a February 2008 release (not CTP, get it here). So, I pressed my luck and installed those. I guess it works. At least it didn't blow up when I tried to create a new web project. Here's the order of events that I did:
- Uninstall EntLib 3.1
- Uninstall GAT July 2007
- Uninstall GAX July 2007
- Re-install EntLib 3.1
- Install GAX February 2008
- Install GAT February 2008
Remember that the GAT is dependent on the GAX.