It's pretty noticable, but that's not to say it will look bad. How much lift do you have? If the 33's fit well, there will be noticable gap over the 31's, but if it's 4" or less of lift, some people are okay with it. I will say that when I downsized the tires on my truck slightly, I felt a little disappointed in the look after running the larger ones.
'95 YJ 2.5L, 5-sp, 2.5" lift, 31" Pro Comp MT's
'62 Willys pickup Super Hurricane L6
Original, disassembled and in slow progress.