I've got my new quad core mini server hooked to my Dell 2309W through the HDMI port at 2048 x 1152 native resolution with no real issues. It sometimes takes it a few seconds to settle down when I switch inputs on the monitor, but once the handshake is complete, no issues.
This is interesting, as my resolution is above the advertised max on the HDMI output of 1920x1200, yet my monitor is reporting that it is receiving a 2048x1152 signal, and osx is reporting the the same. Good thing I didn't order the TB to DVI adapter before trying it. 🙂