Linux is fine for bread an butter ie web/comms/ and office for an average user.
If you dabble in 2D photo manipulation, 3D, video editing, well, on Linux that can be a painful experience. And games..
If what you want is Ubuntu's software centre, installation is fine. If not, its a pain. Eg I muck about with emulation SNES, N64. Even Instaling the latest versions that aren't in the Ubuntu software centre is a pain in the arse, compared with the Win versions.
Stability wise, XP Pro rarely crashed, Vista hasn't-at all- and neither has my Win 7 laptop. It hasn't been my experience that Win is any less stable than Ubuntu.
As for security, I'm not convinced that Ubuntu is any more secure per se, just that less time and man hours is devoted to exploiting its holes. And there must be holes, else why are the security updates being released periodically for it?
I don't particularly like the Ubuntu (Gnome and KDE 4) look and feel either, and I don't think its as fast and efficient as its claimed. I think its the Windows of the Linux world; people use it because other people use it.
And i hate the "re-install after 18 months" release cycle, or go to LTS and possibly end up with a POS like 10.04 where i couldn't even get a mobile modem to work, even though it was fine in 9.04.
IMO MAndriva was the most polished Linux out there.