It's a bit early to pre-order for me. I know they can be cancelled, and I suppose it makes you feel one step closer to ownership, but right now, we know nothing about special editions, nothing about the prices various retailers will charge, and nothing about any pre-order bonus items that might be offered. I'd rather just go into a retail store and buy it on the day, but, if it a special edition can be had cheap with some extras online, that would be enough to persuade me.
Yep, I know, it's GT5 - price is almost irrelevant etc., but if you have the choice, why not?!