Nikon D800 or Oly OM-D?

I agree with this sentiment.  Diaper bag + huge DSLR camera bag = too much.  In fact, it was the extra diaper bag we had to cart with us on Thanksgiving that was the last straw for my old Canon DSLR.

That having been said, if you have the means to get a D800, get it.  It and its lenses will hold their value quite well (assuming you also invest in good glass - and getting a D800 w/o good glass is silly).  Either you'll get it and love it, end of story... or you'll get it out of your system and trade it for a smaller system in the future (with money to spare).  But, IMHO, you'll regret not getting that masterful piece of machinery when you had the chance.

You'll love whichever camera you get.

Cheers!