The key is to watch Nikon. It will be announced after there announcement. No Nikon announcement, no Canon announcement.
I've considered different scenarios with the upgrade. If you plan on selling your 7D/60D/550D, etc, it would be better to sell that now. It may not be sellable by the time the MkIII comes out. Or it will be too low. Just something to consider if you plan on selling used. You could sell it now and buy the MkII. The lower price with the sale of your old cam saves you a good amount of money then buying brand new (3299-3499) and not being able to sell or losing more later.
If you buy the MkII now, then you can plan to sell it a year later, lose a few hundred, and then buy the MkIII which by then will hopefully have gone down in price a few hundred plus may be easily available, more stable (v1.1, etc). Buying brand new immediately isn't always the best thing to do (like cars, tvs, etc). Wait 6 months to a year is something i'm considering. If getting the MkIII suddenly opens up new doors for work, then i would get it asap.
I believe the upgrade will be significant depending on what your work is. For some, it may be nominal. You have to look at that too in determining if you should buy a MkII now (and MkIII later).
