Who-is-in

I'd like to know who (if anyone) is in the space at any particular time.
I'd like to find out by way of the intertubes - on a members-only webpage or perhaps by asking a bot on the IRC channel
it would be great if a screen on the wall showed who was here and their exact whereabouts!

Tracking and identifying people

On entry to the space, a member: -

blogs/tweets their (impending) arrival
- perhaps even blogs their intention to visit (perhaps tentative)
or flicks their own personal members' "I'm here" switch - this is easy!
or picks up and switches on a little wireless device that they can carry around the space - it tracks their movements which can be plotted! It can be mounted in a tin-foil hat!

wireless device

This last one is crazy-mad-awesome and most likely to never get done!

JeeNode - most off-the-shelf and re-usable (£20?) http://jeelabs.com/products/jeenode
the RFM12B http://www.sparkfun.com/products/9582 as used in the JeeNode ($7) 433MHz?
Cybiko - we have some of these - do they work? What can they do?
IM-ME
some other crazy little wireless transceiver (e.g. Texas Instruments CC1110)
plus a microcontroller (if needed) plus battery power
server end: tracking devices, device announcements, polling for devices, special device states - We're half way towards this. Check this graph from within the space to show a count of the number of devices holly has recently seen. It works by counting MAC address - at present it only knows about Holly & Kryten (so as to ignore them), but could in theory be used to associate names with any address. That could be used to tell you which members are at the space and have either there laptop or smartphone connected (if said member chose to add a name against their MAC address),