I've been using 10.1 and I have to say it's been more trouble than it is worth.
My number one complaint centers around setting up wireless NICs. For whatever reason, WiFi has long been a problem for Ubuntu (and Linux in general I suspect). If I had to speculate, I'd say that wireless hardware vendors don't feel compelled to share info with Linux developers.
Number two complaint is that I can't stick just any DVD into the drive and start watching movies. Nope, doesn't work that way. Because Ubuntu focuses on being absolutely free, I have to go out and find various codecs and install various players first.
Those are just the two bigger complaints for me. I love the Ubuntu community and the idea of a free OS, but in the end, Windows is just the best option for me.
Side Note: Apple is actually higher on my list than Linux. However, until Apple lets me build my own box, I'll never use their OS.
I ran Ubuntu 9.10 on a couple of laptops and liked (not loved) it. I didn't have the same problems with wireless, although as I recall it took jumping through a few hoops to get it going. Never tried a DVD, so can't comment on that.
Now, Linux Mint 8.0 (based on Ubuntu 9.10) blew my socks off.
They are up to version 9 right now, but 8 works for me - a nice cross between XP and Windows 7. (
http://www.linuxmint.com/download.php)
Codecs? Got them - I can play ".flv", ".mov", ".mpg", etc. with no problems (even Windows media files). Wireless? No problemo. I have a hidden SSID, password protected router and when I added in the SSID to search for, all it asked was what's the password. Firefox comes pre loaded with links to the community and software site also.
A replacement for Windows 7? Not yet - I like Office more than Open Office, and IE8 more than Firefox.
A good alternative for folks with limited funds and a need for a computer to surf with, get mail, do office-type stuff? Absolutely.