After much internal debate (analysis paralysis) I went with the 24-70L, and have enjoyed every second with it! What made me choose it over the competitor was the colors and bokeh, 2.8 for lower-light, and the build quality. It is just wide enough on my 40D to get decent landscapes and tight enough for excellent portraits (and macro). People say it's heavy and bulky, and compared to other Canon offering it is, but it's not that bad, and once you start seeing your results with the lens, you won't think about the weight again
When I mentioned "competitor", I was referring to the EF-S 17-55mm. The debate still goes on in my head, but the only thing that keeps me thinking about it is the IS. Other than that, the 24-70 just took better looking shots (to me). In addition, the build quality and the reach with the 55mm was a little short for my liking in a walk around. Honestly though, I think I would be satisfied with both lenses.