I'm 99% sure that I won't be. I'm part of the "S" cycle anyway....went from original iPhone, to 3GS on launch day in 2009, to a 4S on launch day last year.
I was well aware that by upgrading to the 4S last year that I would be locking myself in until late 2013 and I'm fine with that. My 4S works great, and does everything I need it to do, plus some.
I can say that the 4" lengthwise screen itself isn't enough of a draw for me to spend an extra $250 to upgrade early. Also, given that AT&T doesn't yet have LTE coverage in my area, I would still only be able to get the same "4G" speeds that my 4S currently offers. And I have zero interest in switching carriers, as I have a plan that fits me well.
Only way I'd consider taking the plunge would be if Apple comes out and hits us with something COMPLETELY unexpected. It would honestly have to be a game changing feature that nobody even saw coming - something on the same pedestal as the retina display - for me to consider forking over an extra $250 to AT&T to upgrade early.
On that note, I'll look forward to the 5S next year when it is announced.