QUOTE(Alex H @ March 29 2007, 01:54 PM) [snapback]106521[/snapback]
Hi there, I own 5d and I need a back up/second camera. I was hopping for new MK3 but it is going to be available in May and it is 4.5K of $$$. I still considering it, since if I get it I won't be changing it for several (maybe 5) years for sure. The other thing is that I might be going to 2 weddings with 1 camera. So what would you suggest - get some camera like 5D, 30D, Rebel XTi, before I get my MK3 or just wait for MK3? How do you handle two cameras with different controls like 5D and MK2/3? Is it difficult? Do you have any problems switching between them?
Definitely don't shoot a wedding without a backup! You just never know what's going to happen.
I frequently use both my camera bodies "at once" during really busy receptions. I put different lenses on (usually something like my 28 - 70mm for my main body and a wider lens on my backup) and hang both around my neck. when I need to, I can quickly drop my main body and grab my other with the wider lens to get shots I want. During the dancing, I often set the shutter speed slower on the backup so I can get a couple of cool motion pics, but then can immediately switch back to a faster shutter for sharp shots. So not only is it a good policy to have a backup with you at every wedding in case of equipment malfunction...it's also just plain useful even when things are going well!
I have no problems switching between my bodies but I use them a lot when I'm not working, just playing around, shooting things I want to shoot. Often its my cats.

Just get used to the controls on your backup, figure out what settings you want to use well in advance of the wedding's start if you're planning to actively use it during the reception. Practice makes perfect!