The problem is definitely switching from 18f to 30f, it has to do a download to change its firmware, switching back from 30f to18f is slightly better but can still give trouble, there are some posts on the MC forum, but most people now just put a ticket in, also there is a file that support posted in one thread, so if you actually brick the pk3 you can take it apart and connect to a small (very small) header inside to reload the boot loader, but get it wrong and its toast. however they will send you a new one. the problem dosnt happen on any other system, just win7 64 bit, and its only when you switch from 18f to 30f, it dosnt always hang, but so far I have bricked 3, 1 had to be replaced the other times I have managed to get a boot loader back on.
Win 8 seems ok, but just does annoying stuff like hang sometimes.
The reason I know about it, is because I was doing a 30f article and 18f project, in the end they gave me a ICD3 because it uses its own drivers. Also using xp in virtual machine on win7 64 bit works fine! actually it works best of all