Some MKII guys mentioned it, here or/and #5.
Some hace mentioned it. Personally I never felt that way. It takes a bit of adjustment to get used to the huge files (comparatively) from the 5DII and if your computer or software isnt ready for the upgrade that can be an issue. The main complaint I heard was that the 5D is more filmlike and that the 5DII was more digital in look, probably due to the weaker AA filter and the less pixel density in the 5D. Also the 5D noise seems a bit more like film grain.
Thank you for the info!