I shoot the 1DS2 personally and use a 5D2 at work. I too, have thought about replacing the 1DS2 with a 5D2. Unlike a lot of other people, I think the 5D2's main drawback is the fact that it's got far fewer selectable AF points. Yes, the low light AF lock is pretty poor compared to 1 series bodies, but if you don't need to track moving objects in night clubs, it's not a deal breaker.
Where the 1D2's AF really shines is the fact that you can choose from so many points. I find that this really aids framing subjects properly in camera. I actually prefer the AF point selection more than the 1D3's (which I also own.) I would think that in the context of your work as a wedding shooter, you're going to miss the flexibility in AF point selection that the 1DS2 offers. Of course, I'm assuming that you shoot that way. If all you do is center point, then the point is moot.
The big plus with the 5D2 is ISO performance, of course. I think the noise levels are better at higher ISOs and you can go higher if you absolutely need to. And while I like the LCD of the 5D2, I actually think that it's deceptively good looking—even bad shots look good when chimping and you might not realize something's missed focus until you view it on a computer screen. This is something that's even more true of the 5D3! One more major thing to mention: 5D2 doesn't have a 100% viewfinder. You'll get used to it in all likelihood, but it's a bit of a shock at first.
Bottom line: if you mainly shoot center point, think you'll get used to the viewfinder, and often find yourself wishing to shoot beyond 1600 ISO, then go ahead and get a 5D2.
) but love everything else, AND it takes SD and CF cards.
