I think it's kinda wierd to beat dead horses, but here goes again.
To all the posts saying, "don't worry, it's only at high ISO," and "you're not going to see it in large print."...
Well, I'm a landscape photographer and a concert photographer. I remember when I used the first 5D as a back-up to my 1DSII for concert photography, and the pain in the butt it was to go through about 5,000 plus ISO 1600-3200 shots of a couple of concerts that all had that wavy set of lines that some reported in the 5D (and I wasn't aware of at the time). I'm not looking forward to dealing with the new "black spot" issue in the 5DMKII, and having to go in and use scripts to fix any issues with stage-lights or intense highlights on the performers (which are all through my concert images).
As for "it won't show up in print," I think that's a bit of a blunt statement. When making large panoramic landscape prints, I like giving the viewer the sense of being able to "walk into the picture" and see the veing in the blades of grass, grains of wood, and fine sparkles in water ripples. Sometimes, this is accomplished by printing at 100% magnification. If people are seeing it at ISO 400, and I was already excited with this camera about being able to shoot cleanly at ISO 800 if wildlife came into the mix...I'm not so crazy about the reports so far.
Am I going to get a 5D Mark II....yes, particularly because of the live-view/high resolution combination. Does that mean I should be happy with this black-spot issue, and wait months for it to be fixed? Of course not. I don't like the fact that the main reason I'm holding on to my current digitals, instead of selling them towards the purchase of the upgrade, is that I'm going to need a back-up not for physical damage or loss in the field, but because I'm not sure I can trust the processing performance of the 5DMKII until they fix it.
Is it possible that they'll have this fixed in the latest firmware fix in the coming weeks? Sure. Is it also possible that it'll take months, and I might be put in a position where I can't send it in to get fixed because I need it overseas for a shoot, and I can't chance waiting for them to return it in time before I go? You betchya.
Yes, it appears to be a wonderful camera. But please don't glibbly dismiss people's concerns. The less we bring these issues up, the slower it will take for Canon to fix.
Pete.
P.S. Here's a couple of shots (on a 1DSMKII and 5D respectively) that might be issues with this problems (sans the black&white conversion on the second pic):

