There isn't a switch for that in SE. (closest would be the anti-aliasing checkbox in the Fonts configuration page. Double check it, but the image you sent looks worse to me than just having that diabled - more like it's rendering assuming a resolution different from the actual resolution).
Qt determines how to do the font rendering based on what desktop environment it detects, ideally so desktop specific settings make a difference. (so for my KDE example, fiddling with DPI and other font settings in the KDE setup actually makes a difference with font rendering in the editor, once you restart the editor). Since it works fine for your other apps, my suspicion is that something about running under the vnc server on Ubuntu 10 is confusing it, and coming up with a pretty poor font rendering setup. I'll have access to a Unbuntu 10.04 system a little bit later this morning, so I'll be able to see what's actually going on, assuming I reproduce it.