Here https://dl.dropbox.com/u/23177754/usocket-ecl-patches-2012-11-18.patch you will find several fixes for usocket that improve integration with ECL.
The problem is that usocket does not list sb-bsd-sockets as a dependency, but rather relies on REQUIRE. This makes it impossible to build standalone applications because they will crash when looking for the files associated to sb-bsd-sockets. Instead, with the current fix, ASDF is now capable of detecting that the library needs sb-bsd-sockets and link the program with it.
Juanjo