I've been leaning towards going FF for quite a while now.
Just like Holden once advertised their HSV's with something along the lines of "I just want one" as the reason for buying one. I want to go FF for no really specific reasons. I just want to go that way.
It comes down to two things.
Firstly, I want to go to FF
Secondly, I need faster better glass for the sorts of night shots I'm aiming to eventually do and whilst the 60D is more than capable of it - even DakotaLapse uses a 60D for some of his stuff - it becomes a case of if I one day plan to go FF, then buying expensive glass now for the 60D and then changing later to FF, means a more expensive changeover later. Yes, some of the glass would work on both, but work on it, and originally be designed for it, are two different things.
If I do it, I'd probably aim to get myself a 5DIII, and a pair of L series lenses to cover the same range my current 18-200 covers, so probably the EF 70-200mm f2.8 L ISII and maybe the EF 24-70mm f2.8 L USM II. That's about $10k by my guesstimates
Massively overkill for my skill level, and way too much to sink into a camera when I'm not a professional, and never plan to be. So I probably need to be talked out of it
So start talking before I do something stupid like go into a store and hold one, to see how it feels, because if it becomes an extension of me, the way the 60D has, and feels comfortable and easy to use, I'll probably do something stupid like buy one.