We used three different cameras while in London (yeah it was a bit excessive but we did end up using all three). The first being the Canon Digital Rebel XTi with that new EF 24-105 1:4 L IS USM lens. The second was a Canon SD-1000 which was being used primarily as a video camera because of it's excellent movie mode (640×480 @ 30fps). The last camera was the Canon S70, my old standby because of it's small pocket size and ability to shot RAW.
The first thing we should have done was check the clock on each camera before we began shooting on the first day. It ended up that the cameras were not synced and when all images are loaded into iPhoto, they are not in order.
I found these handy scripts from Joe Maller for manipulating the dates and times in iPhoto. It's a tad on the slow side (I'm sure because of Applescript) but it does the job.