[update: February, 2009]
It has been 11 months since I bought this lens, and I have used it exactly 3 times. I am not saying I don't like this lens. In fact, I love this lens. It's one of the best built L lenses, and is one of the sharpest. For a macro lens, its also very fast focusing. Like all macro lenses, AF does not work well near the closes focusing distance, but for non-macro use, this lens focuses as fast as any L lens.

If it's such a great lens, why did I only use it 3 times in a year? For one thing, I don't do much macro stuff, but the main reason is that this lens is kind of "slow" for a prime, and L prime no less. I consider any lens slower than f2.8 slow. If I need the 180mm focal length, I would use my 200mm f1.8L instead.

If macro is your thing, this is one of the best macro lenses to have, for the Canon mount. It's impressively built, fast focusing, extremely sharp, and the weight is reasonable. No, I am not selling this lens. It's a keeper.

[End Update]

This is my second 180mm macro lens. My first was a Sigma 180mm f3.5 EX HSM, a great lens for the money, no doubt, but not as good at infinity as I had hoped. Used the Sigma 180 only a handful of times and due to its size and weight and the fact that I have 5 (yeah, talk about LBA) other shorter macro lenses, and eventually sold it. I felt it was hard to justify owning the lens when it was not being used often enough.

Well, LBA (Lens Buying Addiction -- I know, it's not Pentax, but) is back. I am hoping this time, the Canon 180mm f3.5L will stay with me and is put to good use. Being in the middle of winter when I got this lens in Feb-2008, there is not a whole lot of stuff to shoot, in terms of macro subjects.