Just returned from a few weeks traveling by train in Europe. Took only the 5D and the 24-105 as high performance and little weight was desired. I am very pleased with the images I have thusfar processed, which ended up being over 20GB. Praise thee 8Gb SIM cards!
I found the low light capabilities were fine with a tripod, as I had previously fretted the use of the 24-70. Overall, I appreciated the longer pull and the IS but I still hold the 24-70 in extremely high regard. Yes, shooting RAW I compensated for vignetting with CS2 and it is a non-issue in the final analysis in my opinion.