After a while the unity launcher will break (get corrupted?), this now happened for me at around 24 days of uptime. Part of one icon will show near the top of the dock (as can be seen in the screenshot unity-launcher.png), but the actual object is not there. The objects in the launcher do work, but the positions don't make sense. As can be seen in the screenshot, the labels also show up on another position (however they do match what the mouse is hovering over). Also the launher doesn't fully expand, as can best be seen in the sceenshort unity-dash.png.
Unity is fully usable using the keyboard, except for launcher related things such as switching applications by super+<number>. The issue has once also gone away after a couple of weeks, returning unity to full working state. I also restarted unity by killing unity and the compiz processes, but that doesn't really matter at all. Actually this time it occured I have also logged out and logged in again, still leaving the launcher in it's broken state.
My graphics hardware is an ATI Radeon HD5450, combined with the 'radeon' driver. I'm using Ubuntu Oneiric AMD64.
Thanks for the bug report. To try to investigate and reproduce: are the 24 days of uptime continuous? or have they been interrupted by suspend and resumes cycles? Other factors that might explain why the launchers disappear? Have you been able to spot /when/ exactly that was happening?