I have a really old laptop--1ghz Pentium III, 384MB of RAM, 20G drive, lame ATI graphics--that I installed Kubuntu on yesterday because my temporary Vista beta license expired.
Everything went pretty well on the install. For some unknown reason, it launches into a full fledged window system off the CD instead of asking me if I want to just install. Ok. The install was pretty fast, probably twice as fast as Vista. Unfortunately that's more of a good sign for Vista, since it has significantly more functionality than a base install of Kubuntu.
Stage two: I boot it up, it won't connect to my Wi-Fi. Why? Silly me, I didn't follow the instructions on a wiki somewhere that tell me to make sure to install knetworkmanager and a post on a forum somewhere that I needed to install and configure a kernel extension called ndiswrapper. Its all so obvious!
Stage three: Working with it. Has anyone else noticed that the font situation is still abysmal on this OS? I'm trying to type this blog entry from Opera on Kubuntu but it's ... sooo... ugly. Microsoft has definitely done one thing right with their ClearType fonts on XP and Vista. Plus Opera on Kubuntu seems to have a lot of issues trying to keep the text wrapped around in this box I'm typing in. Never noticed anything like that on Windows (though that's arguably an application issue).
Stage 4: This thing keeps hibernating for no reason.
Bottom line is, since I own a Windows license I can just pop back on here sooner or later, I'll probably take it back to Windows or just get rid of the laptop altogether. I'm not sure what the advantage of using this OS would be unless I had to do development for it right now.