I'm on Fedora 15 with www.infinality.net's FreeType patches (basically hinting only in the y-direction, x-direction is ignored, and a few things to improve contrast). I've added Ubuntu Mono to the "TT Instructed Font" list (read: autohint: FcFalse, hinting: FcTrue, hintstyle: 3). I'm not sure how the patches handle fonts that don't contain full hinting instructions, so maybe take this bug report with a grain of salt. The 'thinness' of the font compared to Ubuntu Regular however makes me think that autohinting is active somehow... See attached screenshot with debug characters. Compare the tittles to the ones in Ubuntu Regular (see menu of terminal). They either hang too low or are too small. Or both. The dots on umlauts like äöü look fine.
Side note: fontforge says font version 0.80, sfnt revision 0,799988. I grabbed the font archive directly off the repository server and took the file that had 0ubuntu3 and +console in it, iirc. No idea is this is the newest. I wasted 2.5 hours trying to add the ppa to an ubuntu live dvd until I got tired and opened the URL in a browser. That didn't work on F15 with FF6 but on the live DVD it did. Huh.
Nikolaus: thanks for filing the bug. The "+console" refers to the experimental Linux Console 'setfont' .psf bitmaps, but these would only be built at package build time.
I'm trying to read the hinting debug symbol, which appears to show '33' (thirty-three). Could you try changing the font size in the editor and seeing if this number adjusts, or if it's just an artefact of the left-hand-side being cut off the digits.