I've got a titanium Swift on a bike that gets a bit less than 1000 miles per year. Perhaps 8000 miles on the saddle total. It's been fine.
I should note that I weigh 155 pounds and am not hard on equipment. Haven't even broken the Lepper Voyager saddle with Reynold tubes used for the rails and cantle piece, which are somewhat notorious for breaking. As such, this doesn't tell you much about titanium rails.

I was just looking at Brook's web site, hoping to see what the weight of the titanium B.17 is... but they don't provide that info. Considering that they charge $150 for the titanium rails, I'd have thought that they might want to boast about how much weight it saves over the steel version. Nope.

I'm also surprised that they don't offer the Swift with titanium rails anymore. That was just about their raciest saddle, and seemed like the most obvious to sell in a weight weenie version. I don't get it.

edit: I should have scrolled down further... the Ti B.17 is 410 grams, and the steel B.17 is 520 grams. So a bit more than $1 per gram saved. A good deal?? I have no idea... I bought my Swift used and at a good discount.

Steve in Peoria