Responsiveness under disk I/O

Don't worry, you don't need 200 tabs in Firefox to get this behavior. I get it all the time by just running a few more apps than (apparently) the kernel with this hardware can handle. Often - memory at 50%, cpu low, but IO spikes up and typing an email is going back to the '80s with having to wait +5 sec for each character to appear. Embarasing, considering I have little if anything running that requires real resources or IO (mail, chat, feedreader, few browser windows, text editor, filemanager, calendar - that's it).