I use them a lot, with some very good results (some less so, but let's be positive). How I treat the bids is very simple:
1) if I am not interested and would never be interested (ie just don't find the profile attractive), I just delete the bid, no message back
2) if I like the profile I will message them fairly quickly. Sometimes they bid with a message which encourages you to email back, sometimes they say nothing. The object of my email is to try to make sure that they have read my reverse booking and are happy with what I am after, and also to perhaps start a short exchange of messages so that I get a feeling for whether they are friendly, genuine etc. I make sure to give them a broad view of when I will be making a decision on the booking. Basically it is a holding message to say 'I am interested but I still want to leave it a while before I make a final decision).
I have found this seems to create a good impression and lots of the girls who receive the holding message will bid on future bookings. Hence why I only message people who give me a positive first impression.
If I can give one piece of advice - just pick the person you like best. Don't automatically go for the girl who has reduced her rates the most. I find they are the ones more likely to cancel close to the time.
Whatever you decide, I hope you have a good time. RBs are a mixed bag but i still like using them.
Edit: should also say that a quick message turning down anyone who you don't choose but would really like to see another time seems to go down well in terms of future bids or offers to honour their bid another time. Basically, be polite to the ones you like.