Hello all,
most of what you're all talking about is spelt out in this page:
www.xiph.org/xiphname . It may also be in a wiki or two, but I haven't looked to be honest - I just went to the source (no pun intended!).
In brief, the fish in the logos is a
very stylised version of a "swordtail" (have a look at a real one or a photo and you'll instantly know what I mean

). I also noticed the old heavy-black-lines fishes changed to new no-black-lines ones about 6-12 months ago when they changed the look of their website. (IMHO, the old black-lines version looked cuter than the current no-lines one - more of a "fish in the headlights" look

.) Also, in the new versions the one-fish is for Ogg, and the four-fishes is for Vorbis; IIRC in the old versions a yellow-and-cyan fish was Ogg and a orange-and-blue was Vorbis (now they're all orange-and-blue, just different sizes).
The "dude hammering a snake" thing (based on a Scandinavian myth, see the website for more) seems to be more OggSquish than Vorbis, but as the picture atici found in a previous post shows, it has been used (mistakenly?) for Vorbis in the past too.
Hope this helps and/or is of interest to someone.
rc
PS it doesn't seem to have hurt mp3's case to not have a widely-recognised logo either!