The compass is completely back-asswards. It generally points in the wrong direction and doesn't even rotate the right way. It's never accurate and always disorienting.
It's a known issue with the phone. Others have reported it to htc. If you try Google Sky Map, its the same thing and makes the app useless for the most part. Call HTC and Verizon and report it. If enough people complain maybe they will patch it in an update with Gingerbread!