A little off topic.......I have a 40D and have purchased the 70-200 f4L is and the 50 f1.4. Now I need to fill out the mid and wide end. I don't like big, bulky, heavy lenses for my mostly walk around, landscape work. I'm thinking of the 24-105 L (or the Tamron 17-50 or Tamron 28-75) plus the Canon 10-22 or Tokina 12-24. How do you like your Tamron 17-50 and your Canon 10-22?
I love both the Tamron 17-50 and the Canon 10-22. I purchased the Tamron from B&H in NYC a when it first came out as a general walk around lens, ended up using it all he time. It takes incredibly sharp pictures through most of the ISO range. I picked up the Plastic Fantastic 50m 1.8 II for those times when the 2.8 Tamron was not fast enough for the very low light situations, and to stop motion from my 9 mos old ever moving son indoors. The 10-22mm is also a great lens, and the build quality is first rate (even has a rubber gasket around the mount - not the same as the L but still nice to see). I don't use it much indoors under low light, so the f3.5 was not a big issue, if it was I would have gone to the 16-35 F2.8L. For outdoor work, it is a pleasure to use. Very fast USM, and color contrast seems great to my eye.
On a last note, the 24-105 f4 L is a very nice lens, of course build quality and optics are first rate, but the f4 s leaving me feeling a bit shy of 100% loving it. Now let me state that I had extremely high expectations from this lens as it is "L" glass and cost twice as much as the Tamron 17-50 2.8, and I was expecting it to behave as my all purpose Pro quality work horse, but it has not. Given that I'm still within a period where I can return it, I might get the 24-70 f2.8 L instead and try that for a week or so. I have to really push the ISO on the 24-105 to get decent indoor shots sans flash - I really love the look of non flash shots. They're pretty close in length and weight (a bit more on the 2.8 obviously), and I can use my feet to make up the difference in 35mm reach loss to gain a more versatile shooting lens. Who knows, I may be way off, but for the $1000+ price tag I need to be sure.
Below are links to tests done on the 17-50; they actually rate the optical quality 4 stars vs the 24-105L at 3 stars:
Hope my 2c helps.