Badly thought out system by the sound of it, from the horrors have read RB is not something I would use. the logged in now facility serves me well for late nights.
Yeah, I'm not sure why they make a distinction between blacklisting and blocking really. If I don't want to see someone pop up in a search it seems unlikely that I would want to receive an email or a reply to an RB from them. When you put someone on the block list you even get an option to block auction bids, but that doesn't include reverse bookings - I think the blocking system was probably set up back when the WGs could post 'special offer' auctions (rather than just selling underwear and stuff like they can do now), and they have just made exactly the same system available to profiles set up as 'seeking services'.
However, it is a good thing to be able to block emails. I have occasionally received fairly rude messages from people when I have turned them down for an RB, and it's good to be able to block them and ignore them.
I still like RBs. Sifting through the crap does occasionally get you a good bargain. But if you are after something at short notice your 'Logged in now' approach sounds good.