So I purchased a Brooks B17 Imperial saddle about a year ago. It's a great saddle, but with one downside. As it is made of leather it needs to be protected from the elements, more specifically the rain, otherwise the leather could become damaged.
My initial solution to this was to use a plastic bag. They're cheap, can be found almost everywhere, and they can be stuffed under the saddle when not being used. They are very effective, but have a few flaws. Plastic bags are not very durable, they rip easily. They pretty unsightly/noisy when riding. If you use them on a stationary bike people sometimes remove them because they think that some litterbug has just dumped rubbish on your bike.
I decided to try out an alternative, so I bought the Brooks rain cover. In South Korea they only sell the version with Brooks logo, which is not to my taste. It's a bit obnoxious, shouting out that there is an expensive saddle on the bike. I used a marker pen to black the logo out. Initially I was happy with the rain cover. It kept the seat dry. YAY! Job done.
However, this week I left my bike out in a light wintry rain for a couple of hours. I was confident that it would be fine, but when I got the bike back to my house I removed the cover only to realise my seat was damp. On closer inspection it transpired that the waterproofing on the Brooks cover had worn away, deeming it useless. I've only had the cover for a few months so I'm not all that impressed. I should have saved the money and stuck with the plastic bag.
Living in South Korea I suspect that I have one of Brooks's older rain covers, which Brooks themselves admit were not very effective. Apparently they have since been improved, but I don't think I'll be buying another Brooks rain cover anytime soon. I've got a cupboard with dozens of plastic bags in so I should be fine with them in the meantime until I find a better rain cover.
*** UPDATE ***
I have since purchased a Brooks Flyer Special which included a newer version of the Brooks Rain Cover. The new version doesn't have the giant logo on it, which I think is a great improvement. Also the durability of the waterproof lining is vastly improved. I have cycled many miles on this rain cover during the current monsoon season in Korea and haven't had any major problems. The seam at the nose of the cover leaked a small amount of water, but nothing serious.