Full frame anybody?

I have just got a new OM-D and I am really pleased with the images it can produce.

Also the camera is small (althought not pocketable) and very sturdy and nice to use.

I was pretty much convinced that the m43 clearly won the trade off in size x quality against apc-s Dslrs.

But now with the new Nikon D600, I am having some doubts. Will the trade off between size x quality be also justifiable? Why build up an expensive lens system around a m43, if you can get full frame? I know its more expensive, but not that much anymore...

BTW a really like the OM-D but are you also having second thoughts?