There was a previous thread on here a few month ago asking the same question.
http://forums.rabbitrehome.org.uk/showthread.php?351528-Are-any-of-your-rabbits-microchipped&highlight=MICROCHIP
All three of mine are chipped. For the sake of £10-15, we mostly did it for peace of mind in case they ever escaped.
Whilst not every vet or rescue might scan rabbits, if more people did microchip their rabbits these organisations would start to realise that they would need to scan rabbits as well. If we want to change the ideals of rabbits not being throw-away pets and prevent the 10,000's of rabbits suffering and going through rescues, we need to promote this idea ourselves. Just think how many people believed that dogs and cats should be microchips when it was first thought about and introduced. By next year all dogs will need to be microchipped which can only be a good thing.
I appreciate some rabbits will get quite badly stressed visiting the vets, but it can be done during neutering with no issues. Hershel and Harry were done whilst being neutered under anesthetic, and George was done on his follow-up appointment after his neuter as we had forgot to ask. It did upset George a little bit but no more than trimming his nails do and he was soon over it.