"I think you should at least be able to cancel your reservation. [...]"

well, after giving this some consideration (and checking that it would indeed be only about a dozen lines of code!), i have added the ability to *CANCEL reservations in gridcosm*! -trumpets blare-

thus, i give you... gridcosm engine version 2.8!

and i will be watching the unreserve activity. if there seems to be some kinda abuse going on (like spastic reserving and unreserving going on just to irritate people waiting), i will roll back the change.

oh yeah, and you can only cancel your own reservation; of course.