I live in flip-flops!!
With Old Navy - I have to get 1 (ONE) pair at the beginning of the season and test them out -- it seems like every year something is majorly different.
This year - exactly what you said - the sides hurt bad. So I went shopping around and found some nike ones that I liked. Only got brown and black though!
If I find a pair that feels good, I'll buy in as many colors as I can find/need/afford.
I also try to purge every summer as well. I don't need 50 pairs of flip-flops.
=)