My Xperia S got a swim today, fully imersed during a few seconds.
Got a grab of it, dried as much as could with TP, still working ! I think the covers on HDMI and USB ports saved it. The only real open space is the jack plug which look almost waterproof in www dot sonymania.cz/storage/1331332888_sb_xperia_s_wi.pdf, and the speakers, which have some joints. So, kids don't try this at home, but apparently the xperia S is enough of a compact self-contained tight son of a bitch that it can handle water (probably not prolonged though). Considering Sony made the waterproof acro S, maybe some parts got also in other xperia phones :)
The red water damage sticker got red though, and it's a bummer if I ever want to get it repaired in a few months or something with something unrelated to the swim.