Indeed, as you mention, Lubos: The question is not so much if there are vortex defects out there, but if they are fundamental strings. I guess no one with an elementary knowledge of gauge theory would doubt that there are non-trivial cycles in the vacuum manifold of spontaneously broken gauge theories. Clearly some solutions are going to wrap such cycles. Polchinski et. al. spend most of there efforts on finding a good mechanism to distiguish such gauge theory strings from the fundamental ones. The "whip mechanism" is kind of cool: A little loop travels down the string at 0.9999999c and emits very characteristic radiation -- something gauge strings supposedly can't do. Also the combinatorics and rate of reconnection/breaking should be markedly different, but this is highly model dependent.