Hi Jens,
I'm running r352 and it's still up after about a day.
My setup is almost complete: X10, Z-Wave, Philips Hue, UPnP.
What you can do to help in finding the problem is:
1) install screen (sudo apt-get install screen)
2) stop HG as a service (sudo /etc/init.d/homegenie stop)
3) open a screen session (screen)
4) run hg in the screen session (cd /usr/local/bin/homegenie; sudo mono HomeGenie.exe)
With CTRL+A, D you can detach the screen session and logout.
When it happens that HG stops running again, you can attach the HG screen session with screen -x and see in the console the error that made HG stop.
Also enable logging, there might be useful informations in the log file to better understand what happened.
Cheers,
g.