I have just tried the new Mac OS X VM (Squeak 3.8.20beta1U) and have  
noted that
when saving image located on an nfs mount, all the system is blocked  
probably on a network lock.
When saving image located on a local disk all seem ok.
When using Mac OS X VM (Squeak 3.8.18beta4U) and saving image located  
on an nfs mount, it's ok.

My system:
- Mac OS X 10.4.11
- Dual 2.3 GHz PowerPC G5

Best regards.
Alain