OK. I've actually been thinking about this. I can't definitely remember what it could be, but have come up with two possibilities:
1) Looking back at some of my old posts, I think I was in the process of starting up another 'reality' type game in one of the forums akin to the one I did on The Mole. Maybe it's just hind sight playing tricks on me, but before I left I think that could have been 'something big'.
2) The other theory is that the 'big thing' was my massive leaving announcement in Other Chat, which I had the displeasure to re-read and cringe at a few days ago. I imagine that I was fairly disillusioned at the time, rendering this the more likely scenario.
But we'll never know for sure!
Thank you for the welcome, Andy. I'm sure some consensus will emerge on what to actually refer to myself as, as the weeks and months go on.