Hi Mark,
Interesting idea - I think between most of us we have quite a bit of kit (lenses, rails, extension tubes/bellows, reversing rings, flash etc).
Of course, we'd need a few subjects, but that's not hard
A few of us have reasonable macro experience, and MattC gave a nice overview at our camera club meeting a few weeks ago.
Guess we could treat it as a workshop - so if anyone else is interested send a PM or post something here and we'll see if there are enough numbers.
Cheers
Chris