My Experience
I have the Leica 90mm f/2.8 lens that was made from 1990 to 2008. I bought it about two years ago, but haven't used it much--although I dreamed and searched for one at a good price for two years.
I prefer wide-angle lenses like 21mm and 35mm. When I have used the 90mm lens, though, I have been surprised at how well it performs. It does particularly well at portraits, which I would not of thought to use.
I bought this lens at an amazingly low price, for about €500. It was in great condition, but had some specks of something inside. It also didn't have the 6-bit coding on the lens flange. Last summer I sent it to Leica in Solms, Germany. They charged me a good bit, but they took apart the lens and cleaned the glass, and aligned the lens. They also put a new 6-bit encoded flange on it and replaced the red alignment dot that was missing. It's a much better lens now, and still cost me less than I could sell it. So I'm very glad to have it.
I really should use it more. It's such a nice lens. Well, at least I've taken care of it.
-Russell