oh this is very useful. I also had the same question.
mine came with a 750mA (.75A) charger. As I left my charger at home during the holidays, I had to make due with one that I bought from a nearby tech store. I was very happy with the charger that I bought as it charges my phone really fast. I found out that my new charger was also a 2A model.
so I guess, in my experience, I noticed a big improvement in charging speeds comparing the 750mA with the new 2A charger. But I guess coming from a 1.2A charger, it only makes little difference.