SealSkinz waterproof socks, modeled elegantly by me with the Solent Galley Bembridge at Emsworth, whence we had rowed in search of beer. Sorry about the dismal mobile phone picture quality.
The socks have an inside layer of GoreTex or something that keeps liquid water out but lets water vapour through, so you can leap out of the boat confident of keeping your feet dry but not get into a massive sweat when rowing, as you can wearing wellie boots. Hi-tech indeed, but also the most expensive socks I have ever bought - the thick end of £30.
Combined with a cheapo pair of sandals they worked brilliantly, though I was surprised by the amount of gravel that got trapped under my feet.
In fact I got overconfident and stepped out of the boat too early when we got back to Langstone. I went in up to my knees and immediately discovered that the sock tops do not seal. Drove home with soggy feet. Damn.