The existing problem (for Jeff) is that it is hard to find modified or improved versions of the same snippet. Whereas a URL points to an inidividual snippet, the GUID could point to different versions. The same GUID could also be used for the same snippet in a different language.

Obviously you could also group related snippets on a site, but that formalizes it too much. Snippets are mean to be copy/pasted and passed around on forums, blogs and sites.