My default summer and boat shoes are $8 river shoes. Very close to barefoot, but a great grip and some protection against stubbing your toes. They dry out very quickly too.
The only time I put real shoes on in the summer is when I have to do some serious work, or dress up for something.
With full time use (100+ mile bicycle rides, volley ball tournaments, walking, swimming and other activities) I get about 2 years per pair.
ken.