I know it was several months ago, but it has recently come to my attention that there was someone in an Ariel costume at San Diego Comic-Con this year. bri_chan was there dressed as Alice in Wonderland, so she of course hung out with Ariel (and her friends in the "Sexy Disney Princesses" group). Bri_chan has posted some pictures, so you should click here to see them now! (And I found one on Flickr, which you can see to your right.)
Back? I'm not sure how well the attempt to make the Ariel costume "sexier" by adding cutouts to the fin to make it look like a garter and hose worked. Sometimes it's nice, but other times it looks silly.
To give credit where due, this Ariel cosplayer's name is Christy, and she's on LiveJournal as rebel__princess