yes, cool idea ;-)
faintly reminded me of the ID3 "genre" tag for Mp3s.
of course, the decision which musical genre a file represents is subjective.
But if Gnutella could search files by that tag, the results would still be averagely good because there is something like a "mental common ground" of users.
Same applies to the user interest groups- pools of interconnected users sharing the same interests would certainly form!
if it was possible to combine the group-by-interest feature with gTLD filtering, gnutella queries would no longer resemble searching for a needle in a haystack.
let's see what the developers think about all this......