I haven't figured out exactly what causes it, but occassionally I get a message that the SB2 finds a Slimserver name already in use, and it gets renamed (in my case, eg.: iMac-8 gets renamed as iMac-9, etc). So I usually have to do something in the network setup to re-connect.
Not sure what causes it yet, but it has something to do with when I re-boot my computer or something like that...