Bosk, your question is about Ubuntu but like several others here I'll stretch it to Linux in general. I've been using SUSE for many years and just upgraded to version 10.2 from 10.0. I've tried a couple of releases of Ubuntu and found them very appealing, and it comes highly recommended from at least one other friend who likes to sample distros (and keeps me well supplied with things to try). I think my preference for SUSE depends on a few factors, some of which won't be of use to you: it deals with some hardware that other distros seem to have a little trouble with (I run a 64-bit Athlon system, so that may be part of the problem); it has a very good administrative utility (YaST); it uses RPMs for package management (though Ubuntu may have an even better system); and finally, I'm familiar with it and know where to find things.
More generally, I use Hamrick Software's VueScan on the Linux machine with my Nikon LS-2000 scanner and have had excellent results. (I've used it with my flatbed scanner as well, an Epson 4990, under Windows, and was able to compare it head-to-head with SilverFast and Epson Scan. I liked the images I got using VueScan best by far, though I'm sure tweaking the settings would enable me to get fine images from any one of the programs.)
SANE ("Scanner Access Now Easy") is the standard Linux scanning software, and I think it can be used as a back-end to other interfaces. I gather it's very capable and it should support the Coolscan well. (I got started with VueScan because it supported an antique film scanner that SANE wouldn't, so I'm not as familiar with SANE.)
If you do go the Linux route, I suspect that other distros might require the same tweak I had to learn to use VueScan under SUSE: Unix and Linux systems have a branch of the file system called "/dev" (for "devices") that contains "files" representing all of the hardware in your system. On my system the device files representing SCSI-attached scanners were unfortunately set so they could not be used by anyone other than the "root" ("superuser") account. (This account is the all-powerful account used to administer a Unix-type system.) So as root I have to issue the following command after each reboot (which fortunately isn't that often with Linux):
chmod 666 /dev/sg*
This changes the mode of the scanner devices to one which allows reading and writing by all users.
The Coolscan IV is a USB scanner, as I remember, so the story may be entirely different for it.
I hope this doesn't scare you off of the Linux route (or Unix -- FreeBSD, OpenBSD, and NetBSD, three descendants of the original Berkeley Unix code, are superb systems). Though I doubt I could get NikonScan to work under Linux, I'm very happy with the setup I've got. I use the GIMP (GNU Image Manipulation Program) as a Photoshop substitute and I like it; an alternate interface called GimpShop makes it more Photoshop-like. (You'll find a LOT of "alternate interfaces" available on Linux.)
Other considerations: Ubuntu comes with good support for multimedia; SUSE is a bear to get to support DVD playing, mp3 encoding, etc. Setting up printing will either be a breeze or eternal torture. (Ubuntu recognized my old LaserJet immediately. SUSE has given me a good deal of grief but I've got it set up at last.) It might be good to look into color management capabilities of any system you try. I'm lazy there; I keep the old DeskJet I use for photo printing connected to the Windows machine and print through IrfanView, which works for me. I'm sure there are far more sophisticated solutions. Graphics pros swear by Macs, I gather, though Macs don't do some other things I need (like run the stat software I use in my day job).
As you can probably see by now, this could all be a new adventure for you. But then again you may decide that photography is enough of an adventure without the adventure of system administration!
Good luck...
