I haven't joined yet, but have had about a dozen enquiries. None of the first bunch were of any interest - they seemed to be from people sending messages to all rellies with a particular name with no qualification. However, in the last week, I had a message from a lady who sent me a census transcript that was invaluable as it was for a very common name. This relates to one of my brick walls and I was able to go back a further three generations in no time at all as not only diid I have the names, I had the places of birth of the parents, hitherto missing.
I think it's definitely worth leaving your data on GR as it only takes one contact to provide you with some information to make it worth while.