I've messed with Linux ever since 1994 or so before they had a 1.0 Kernel release. Since that time I've become more of a fan of BSD systems but that's another discussion..
I would say Ubuntu is the most 'Mac-like" operating system out there that I've seen without buying a Mac as far as system install and upkeep goes. I am fairly impressed by that and their update system works well. So does their packages/software installer system for adding software from the repository.
That said I could never see myself using it day to day as my desktop machine. I like my Mac - I like Photoshop, Aperture and my other commercial + shareware apps way too much.
If my only options were Windows or Linux, I would use a Windows machine offline for photo and do my web browsing/email/etc with an Ubuntu machine.
Currently I do have a machine running Ubuntu with Vuescan to run my Coolscan LS-5000. I did give Gimp a try to do simple retouch/editing on scanned images but it declares that it does not support the 16 bpp images I have scanned and downsamples them before opening so that did not work out. Files get transferred via ethernet to my Mac. Unfortuantely, last I checked, Bibble will not open the DNG Raw files that vuescan can create, either or I would explore that route more. (though it would most likely work on the .TIF files I create)
Anyway, my take is it's not ready for prime time for many things. But depending on your needs it can be pretty useful. IMO, when companies like Adobe take note and start supporting it, then it will be ready. Some day the Linux Kernel and the standard libraries are going to have to mature to the point where commercial developers have a more stationary target to aim at for development. It's just such a mess right now trying to make a complex app that runs well under every Linux distro out there..
If you are happy though - I'd suggest you look into a copy of vmware to run your windows apps in a window on your Ubuntu machine.. Maybe then you would find yourself moving your copy of Ubuntu over to the newer, faster machine and become even happier.
