First: I just read the experiences from a long-time Minolta shooter who got an A33 from Sony to play with for a couple of weeks. Getting stuff for free (without any advertisement money hanging on to it) is liberating as it allows critical judgement - buying equipment usually impairs one with the "of course I made the right choice, I'm not an idiot" syndrome.
He didn't like the EVF. Yes, it's one of the best EVF's out there. But it's still a long way to go. I played around with it at the Photo Plus Expo in NYC and it performed well, but take it outside (as my tester did) and the known issues of EVF (suckiness in high-contrast situations) immediately raised it's ugly head. Also, metering info and other status text is superimposed over your image and blocks your view. I suggest taking a real good look at the viewfinder before committing.
Second: granted you haven't vested a lot of money into a system but switching is an expensive hobby. Keep in mind that your Nikon lenses will do just as fine (or bad) as Sony lenses on the NEX - they both need an adapter (Nikon lenses might not autofocus but neither will the Sony lenses)
Third - one thing that is attractive about Nikon is the large second hand market. Sony doesn't have that to the extend that Nikon has it - Minolta's alpha mount never had the market share that Nikon's F mount has had.
Four - the Sony flash system is wonderful (even in the cheapest models the popup can be a "CLS" master, and once the camera is in master mode you can simply slide a flash onto the hotshoe to "program" it into remote mode. How's that, Nikon?). But the flashes are expensive and the non-standard foot, superior as it is, is a pain in the rear-end because it's non-standard.
Five - Lenses. Sony has a smaller offering than Nikon, and expands their program even slower than Nikon. Don't get me wrong, the glass is excellent; Sony's 70-300G is better (and more expensive) than Nikon's 70-300VR, there's no Nikon equivalent to the superb 70-400 and then there's all the Zeiss glass. And the 135STF makes the Nikon 85/1.4 look like a cheap toy when it comes to bokeh. But... the program is limited. Their 70-200 is outrageous expensive (same price tag as the Nikon version but it's basically a 80-200 - VR is in the camera after all) and getting old, and no hints of a replacement. And although the situation is rapidly improving, there's less choice from Tokina, Tamron and Sigma as well.
Don't get me wrong, Sony has a great system and I actually recommend it a lot to coworkers. But if you already have a Nikon you're going to lose money on selling the existing camera and replacing it with a Sony. Your "great deal" will neutralize that and likely keep you at "break even" but then you lose a large attraction of Sony: the low entry price (yeah I know, long term... but the people that I recommend Sony to are not the ones likely to buy additional equipment).
In general, switching for the sake of switching is a bad idea and this seems one of those cases. If those Sony tours come on a regular basis and you can be pretty sure of a 20% discount all the time, I'd say go for it. But if this is a "once in a lifetime" deal I wouldn't switch.
