I've been using RealVNC Server on my Mac for years, since it gives me encryption and other features used by RealVNC's clients for iOS and Windows. Once I upgraded to Lion, though, it broke. Now, I see a completely black screen while connected. The cursor moves around fine (which I can see while seated at the monitor, and used as an ad-hoc mouse when Lion initially didn't pair with my Magic Trackpad), but no image comes through.
I only discovered the problem with the built-in VNC server when I tried falling back on it to temporarily replace RealVNC.