I've got a reg bag from Deep See. Back when I first got certified, I used to pack the regulator in there snug as a baby before and after every dive. Over time, I came to realize that when driving to the site, this offered no better (and arguably) worse) protection for my reg than wrapping it in my wetsuit (or in my undergarments when diving dry).
One place where a reg bag is handy is in travel. I have a small, briefcase-sized bag that is heavily (3/4 inch) padded - it looks kind of like a really skinny laptop bag, maybe. Inside of that, when I am going on a dive trip, I pack my reg, mask, light, and a couple of other small things. It works well for travel, and you feel a whole lot better about knowing you have the gear with you, safe andsound on the plane, rather than being abused by the baggage handler.
~W