If you can get in on some of the low price 5D MK II deals mentioned in the forum, you will not lose any$$ if you upgrade in a year, so I'd get a mark II. Its going to be popular for a long time.
I sold my 5D MK II this week, and am going to the MK III, but I have lenses, batteries, flashes, all the extras which will work with my MK III, so the price difference for the new body is my only cost.