I've already got a 3DS, will get a WiiU within 6 months of launch and will get a PS4 when it get a game I consider 'must have'.

Day 1 for Wii U, and I'll probably pick up a PS4 Slim. Unless there's drastic changes I'll be staying away from Microsoft again.

a will get what ever comes out first..

I'll probably get a WiiU between its first year, but it will depend on price, games and whatever can happen (3DS' first months comes to mind).
If I get a nextbox it will be 1 or 2 years after launch, as I don't want any surprises regarding faulty hardware.
As for the PS4, if it is backwards compatible with the PS3 I'll buy it soon, if it's not then I'll wait until it has enough games and a price that makes it appeal to me.

In the end I'll probably get a WiiU within its first year and one of the other two 1 or 2 years after their launch.

I will be buying WiiU day one, I will get Nex-Box within a few months of release (If finances allow) and PS4 if and when software comes out that I need to own!

Fact is I always buy Nintendo's platforms day one. Mainly because I know that Nintendo makes my favorite games. This means that I don't need to worry no matter what the games I love are coming. The hardware is a must because I also want to show support and encourage Nintendo to manufacture more units and churn out more software. Unlike Microsoft or Sony Nintendo's hardware is usually reliable day one with few bugs and glitches.

Microsoft has been a must buy too. I love Halo and other franchises available on Microsoft's consoles. However unlike Nintendo I don't purchase Microsoft's consoles day one. I will wait a few months to make sure the software is perfect and the hardware has been perfected. If the Nex-Box starts fires and blows up then I will be aware of that before purchasing.

Sony, I love Sony consoles to a degree. But don't love all too many of there games. I bought my PS3 about a two years into its life cycle thinking there were enough games I would enjoy. Unfortunately I found I only purchased about four games because the others just didn't meet my expectations. Great games but I have been on a budget and have to choose only the best of the best and unfortunately Sony's software while it was the most impressive visually weren't more enjoyable then the content Nintendo provided or Microsoft. I plan to buy another two Sony titles in the near future. But next generation I will hold off on purchasing a PS4 until it has the exclusives I have to have!

My policy is usually to wait until the first price drop. You pay less and you actually have some games to play. All in all a much better deal IMO.

I will buy one of each and sell them.

I will not have one for myself until RPGs start getting released.

I own a 3DS and still only have 1 game for it (the waiting game :P ); I already have Mario Land 3D and Mario Kart 7 pre-ordered and I think that is all the 3DS games I find interesting before next year... kind of sad, but at least it plays DS games.

I am buying a Vita day one.

I am very uncertain if I will even get a Wii U (unless it get a large exclusive game library or drops to a very cheap price, both seem unlikely at this point in time).

PS4 and Xbox 720 are completely unknown, anywhere between day one and never purchase is possible for both of them, just depends on what they actually end up being. (though PSN being free swings some preliminary votes, nothing is concrete at this point in time for my purchasing decision).

First day maybe, pending on launch titles.

Im gonna wait atleast a year to see what games each console has out that appeals to me more!