I'm messing around with Ubuntu Hardy on a Dell Latitude D400 that got a new lease on life with a refurbished keyboard, battery, hard drive, an extra 1G of RAM and new rubber feet. Hey, the rubber feet are important. The times may be tough, and this little box may be old, but I won't send it out into the world unkempt. It's served me very well since 2004, I owe it that much.
Anyway, so far Ubuntu's been great, but things occasionally do seize up on it. Frozen processes that refuse to obey a regular shutdown order -- you know, the click on the x button in the upper right corner -- can be killed the Unix way: with xkill. The details are here. Other solutions -- some gentler, some harsher -- are also described, but this is my favorite.
So, my recap: in the "Run Application" dialog box that opens in response to Alt+F2, or in an open terminal, type
xkill. This turns the mouse into the x of death. Move it over the non-responsive window and click it. It's very satisfying.
Speaking of resurrecting old gear: if you have such designs, and you're a fellow Dell customer, consider Renwerx Tech. They may refurbish and sell parts for other brands too, but I know that their Dell section is superbly laid out. I gave Dell first dibs, seeing how they had a record of what equipment I owned, and thought they'd match my parts searches properly. I only went looking for alternatives when they blithely tried to sell me a French Canadian keyboard.