Peter,
you have summed up the challenges of an exhibition/conference very nicely and I fully agree. My hack room suggestion assumed that there would be some hack time before booth setup or after teardown, and the occassional 30-minute hack session, maybe once per day. Leaving one person alone to man the booth for extended periods of time is definitely not a nice thing to do.
That said, having an intense coordinated hack/review session via IRC and mail for one weekend may be a useful preparation or followup to the Prague meeting. IMHO quite a few things get stalled because our turnaround times are often pretty long, and switching the mind in/out of development mode takes some time which can't be used for development. (Well, that's what is killing my productivity if I only have ~1 hour spare time and spend lots of it getting familiar with the code again before I can respond to reviews.)
Regards, Carl-Daniel