I have 12.04 as a primary work machine, used every day for everything.
Negatives:
1) Hardware support – still not quite there. nVidia Optimus doesn’t work properly, I can’t use external monitors and reboot unless I disable it.
2) Decent power mangement had to be installed and configured by me, it wasn’t there out of the box.
3) First installation suffered mystery crashes and freezes, possibly due to attempting to fix point 1 – eventually had to reinstall
4) A few niggly things lacking like for example, if you put a machine into standby it doesn’t then hibernate a few hours later, like Windows does. This is a handy feature for work reasons
5) Sliverlight (which powers several online video players including but not limited to the Eurosport one) – forget it. The dodgy copies didn’t work
6) Mouse wouldn’t stay paired until I buggered about with it.
7) I miss MS Office, a bit.
Positives:
1) LUKS encryption is a billion times better than PGP whole disk. Indirectly, this means hibernation is usable unlike with Windows + PGP
2) Ubuntu software centre – thought it was a gimmick but it’s brillant to just think ‘hmm I need X’, type it into a box and a minute later it’s up and running.
3) After the reinstall, it’s stable and starts up pretty quickly. Although oddly takes a bit longer to shut down than Windows.
4) Having a choice of desktop environments is fun.
5) Overall, the bundled desktop wallpaper is better. Windows has some real artistic highlights but the photographic ones aren’t as good.
6) Disk usage is a lot more sensible.
7) Overall it’s snappier in use despite a few waits for the first running of some things.
9) Google Earth just will not work