I'm running build 101 both at home (Media Network Server running) and at work (Media Network "Client"). If I bounce around in the network playing a variety of tracks (even bounce back and forth between just a few) it usually starts playing very quickly. But once in a while it takes a really long time (about 13 seconds) to start the track (and the "client" instance at work is locked up until it starts).
The delay is bizarrely constant - I can start counting and am nearly always at 10-13 when it starts.
I've tried remote desktop connection to my machine at home so that I can watch both the servers "activity log" while the work machine is making requests. When I make the request and start counting nothing appears in the log until I've counted off the delay. Then a new line appears that says "Writing" and starts counting up "served"; at the same instant the music starts playing.
I think the next stop is to get netmon running on the server machine and see if anything is arriving "quickly" or whether the delay is in the network.