In reply to Cerris90:
Wonderful idea. Good on theory, poor on practice.
So lets imagine there is such a site.
1. You've got to make everyone/organisation whose going to use a crag to actually forwarn, post the fact that they are going to be using the crag.
2. Different crags will have different 'saturation' points which not every other user will know.
3. How will I as a non user know for example how many people 'Poseur Crags' can take.
4. Then of course you need to ensure that those that potential groups using the system
actually look up to see whether its been booked or not.
5. And this is my real objection - it will simply become a booking circus. Some outdoor centres will simply pre book 'their' crag, weeks, months in advance, and are unlikely to then cancel advance bookings should the need arise.