Edit: This is a GCC bug; compiling the code with GCC 4.5 solves the problem, but only with SFML built as shared libraries.
When linking CSFML in Ubuntu, I'm getting this error:
..
/usr/bin/ld: /usr/local/lib/libsfml-system-s.a(Clock.cpp.o): relocation R_X86_64_32 against `__gxx_personality_v0' can not be used when making a shared object; recompile with -fPIC
/usr/local/lib/libsfml-system-s.a: could not read symbols: Bad value
...
This happens whether SFML is compiled as a shared object or not. The libraries certainly exist, but they appear to not work properly.