I've had the same issue. I posted about it over on xda
I've got an open support ticket with HTC on this issue. I think the issue is some app isn't cleaning up after itself. I've had to uninstall less important apps, to make room to update the apps I care about, but the space just ends up getting filled up again. For comparison, I have a Cliq with CM7; in total, it has 256MB of storage and I can update apps just fine with 30-40MB free. With the Amaze, it stops allowing app updates with ~300MB free.