It's possible something is wrong with your virtual machine. On a clean system to run bitcoind 1GB should not cause the process to die. Check also your diskspace assigned just in case.
There is nothing wrong with my system. I have no swap (thats the main reason) and other running daemons (no clean system). Additionally there is a memory leak on bitcoind. There is no memory leak on other crypto cur. daemons like namecoind. Namecoind releases the memory it reserves.
Memory usage of Bitcoind: 10%
Memory usage of Namecoind: 10%
1 Week later
Memory usage of Bitcoind: 40%
Memory usage of Namecoind: 10%