If you still use Ubuntu 10.04 (like I was) and have the following conditions :
- running Wine applications
- have Intel Graphic Card
Do Not Install | Upgrade Ubuntu 11.04 Natty Narwhal. Or you'll have this black patch bug in your Wine apps (see pic below). This bug was introduced in Ubuntu 10.10 (or so I read) and survives, a very resilient bug this one.
I only tested this on two Wine applications : Amibroker and HOTS (an online stock trading app), they are both affected even on latest 11.04 update.
Upgrade or not to? It's your call of course.
keyword : reason not to upgrade, ubuntu, 11.04