I've been running OS X since 10.1 came out on my iMac 500, 640 MB RAM. I have a cable modem, use Photoshop 6, Filemaker 5, Office 2001, and SoundEdit 16 in Classic, and IE 5, Limewire, iTunes, iMovie in OS X. Have a tapedeck plugged in via a Griffin iMic to rip MP3's of analog music, have a Macally keyboard and two-button mouse with scollwheel, and an Epson 777i printer. I also have a Linksys router which I use to set up a LAN when I bring a Wallstreet or TiBook home from work.
In the 4(?) months I've been pounding on this machine, I have NEVER had to force restart. With the exception of software upgrades/installs that have required a restart, the machine is always on.
At work my G4 400 256 MB has been running 10.1 for about 3 months. I use this machine to test software in Classic and troubleshoot Quark 4, Illustrator 10, Office 98, Filemaker 4, Photoshop 6, Outlook Exchange client 8.2.2 and 2001, Citrix client, and BBEdit. I've had to force quit apps (usually Microsoft apps when going from Classic to X), but no kernel panics.