I installed both Ubuntu 10 and 11 on my HP notebook. The first thing I noticed was that the Internet was very slow. Especially when downloading from their app store. The app store is great, by the way; download speed aside. I also did not like the lack of native support for many popular applications. There are alternatives to many of them, such as OpenOffice instead of Microsoft Office, but some things, like Adobe Photoshop, do not (yes there is GIMP but honestly, it doesn't hold a candle to the King of Image Editors.) Otherwise, many apps worked with it; unless, of course, you want games. (Note: you can run Windows applications inside of Ubuntu using WINE or something like it but it just isn't native performance or feel; the integration just goes down the tubes. Now, I will admit there were positives, like I really liked the app store and the abundance of FREE applications and the little wireless widget at the top, the easy customization and skinning, but it also didn't feel as safe. Where is my SFC command? and my Restore Points? and my Recovery CD's? (If you haven't figured it out by now, I use Windows 7.) I will admit there are some great things about Ubuntu Linux, but it's a little half baked.
Installation was absolute hell. Installing Ubuntu 10 worked fine using the Wubi installer, but version 11 was a different story. I don't even know how I got that working. Of course, version 10 made me compile a wireless driver myself, which was awful, so I quit. Havent touched it since. Windows 7 all the way.
Linux is a great idea, but it ain't no Windows or Mac OS X, but someday it will be up there.