After several iterations of not getting around to upgrading Ubuntu, and subsequently deciding that I may as well wait for the next version as it's nearly here now, I finally upgraded to Ubuntu 10.10 this week.
All was going well, until I tried to play Minecraft. I couldn't be bothered finding a mouse, so I was going to play using my laptop's touchpad. At first, it seemed to be working fine - but then everything was very jumpy, with my touchpad input seemingly freezing up and then jumping around. I figured it must be either lag or something wrong with the version of Java I was using, but then, on a whim, plugged a mouse in. The mouse worked fine.
I didn't think much of it at first, thinking that it's not a huge deal if it's just Minecraft - I can use a mouse for that. Then I noticed that it was happening everywhere - even on the desktop. I wondered if there was something wrong with the touchpad driver, causing it to lock up whenever there was keyboard input, but soon discovered the real culprit - a new setting, and its default value.
To fix the issue, all you need to do is untick the "Disable touchpad while typing" checkbox on the "Touchpad" tab of System -> Preferences -> Mouse.
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