Richard Pyle is able to share some valuable information:
http://www.bishopmuseum.org/research/treks/palautz97/rb.html
One of my favorite quotes from him is that after 10 dives on an RB, he thought he knew everything. After 100 dives, he had some questions. After 500, he realized that he really was a novice.
RBs are great. They can also kill you MUCH more quickly than simply running out of air on open circuit. I would not even consider looking into them until I had a solid 200+ dives in a challenging environment (most Cozumel and all Club Med dives don't count).
They are a very valuable TOOL for the diver, but you have to ask what your reason for wanting the RB is. If it is to extend your bottom time, then nitrox is an answer. If it is to extend your gas supply, then a bigger tank is an answer. If it is to reduce your decompression time, then multiple tanks with multiple gasses is an answer (and an answer that provides plenty of redundancy in the even of the failure of a regulator).
If bubbles are creating a problem for photography/videography, then an RB is a viable answer.
If you are doing extremely long cave penetrations that cannot be done on traditional double tanks with stages, then an RB is a viable answer.
To want to use an RB because it's a "cool toy" is just as "wrong" a reason as to want to dive to 150ft just to dive to 150ft.