IMO, the two big negatives are:

1) The battery life (get the external charger that T-Mobile sells; it's not perfect, but it does help)

2) Lack of Tethering.

There are some other small things (Google Reader doesn't allow shortcuts nor tag editing, Gmail has a few missing features, there's no SyncML client for Calendar yet, the SSH and VNC clients (3rd party) doesn't completely work together, and the IM client lacks some things).

But the two big ones are the battery and the tethering.