UPDATE: (8/21/2011) HippoRemote Pro 3.3 restores support for Screen Sharing connections.
For those of you making the jump to OS X Lion, please install HippoConnect. It is the recommended way to enable connections with HippoRemote. You can download HippoConnect here.
If you previously used HippoVNC for Mac, please disable the system server (if it’s running) and uninstall.
If all you ran before was Screen Sharing, I highly recommend you install HippoConnect. Lion makes a number of changes to Screen Sharing that are great if you actually want to share the screen to a remote location, but not so great if you just want to simulate a keyboard & mouse like HippoRemote.
I’m working on improving support for Lion’s changes to Screen Sharing, but in the meantime, HippoConnect is the way to go.