I have somewhat narrow feet (not enough to actually buy narrow widths, though) and I buy my regular size 7 in Aquatalia's.
I have three pair. Two are size 7 and fit great, and one is a 7-1/2 because they were on NAS and that was the only one left in the company at the time! But they are too big even with a thick sock...I just deal with it.
So I think it depends on the shape of your foot...if you have narrow-ish feet you might want to keep your same size.