I bought the 16-35L II several years ago because the sale price was too good to pass up. I didn't use it much for about a year. Finally I decided I had to learn how to use this lens so I went out regularly with only the 5DII and the 16-35 lens. That forced me to work out how to use the lens.
At first I was a bit frustrated because you have to look at things differently in order to see the shot opportunity. Many of the best Photojournalism shots are taken with this lens, or other ultra-wides. Check out: http://bit.ly/Yj8uzuhttp://bit.ly/XNBfa2
Google photojournalism awards and you'll notice a lot of ultra-wide shots.
Long story short, it became my favorite lens, and I rarely leave home without it.