I'm experiencing also Unity crashes, while not even loading the main menu of Desktop Dungeons.
Some information:

This is the Unity loading screen. The black bar will keep loading till the bar is fully... uh, full. 100% loaded. Then the problems start.

This is my Dock, focused on Activity Monitor. (Task Manager if you prefer to call it)
- Green is free RAM
- Blue is inactive RAM (RAM used by applications while idle, etc... to increase performance when getting used again, but can be used if there is no free RAM anymore)
- Yellow is active RAM (RAM used by appications)
- Red is wired RAM (which leads me to believe that this is the part that the system itself needs)
At this point, actions like taking a screenshot is very hard and the system doesn't respond well. My hard disk (?) (Or another part of my Macbook that makes cracky noises) can be heard.

After a minute or so, this screen comes. The system starts responding again, RAM is made free and Unity is crashed. Taking screenshots is easy again.
My system:
Macbook (white), early 2008
- 2.1 GHz Core 2 Duo
- 2 GB DDR2 RAM
- Intel GMA X3100
My webbrowser:
- Aurora 7.0a2 (basically Firefox 7 alpha)