I had one and didn't like it. Reasons? Well I found it comfortable enough when new, but nothing special. Once it was well broken in I did not find it very comfortable at all. I prefer a plastic saddle with minimal padding. I just didn't see any magic about the Brooks. It was fairly expensive, VERY heavy, and nothing special comfort wise.
I find it interesting that when on tour I met lots of riders and Brooks riders were few and far between, but on the forums that seems to be all you hear. It sounds like no one would tour without one based on reading the forums, but out on the road it was a different story.
If it works for you fine, but it certainly isn't the only answer.
I tend to be very tolerant of saddles and usually have been happy with whatever saddle came on the bike as long as it wasn't wide or heavily padded. In the grand scheme of things the Brooks that I owned was one of my least favorite of all the saddles I have used.