Linden Lab implied (though didn't actually state plainly) that the advertisements were not intended to cause confusion between Second Life and Avatar.
Since about Christmas (just after previews showing the blue-skinned Na'vi began to become available to the general public) IMVU started running some blue-skinned ads of its own.
It was when we saw the blue-avatared IMVU advertisement that sprung up during the same period that we inevitably started thinking about Sea Monkeys.
There's more similarities going on here than just the visible, so let's rummage around and see if we can't find one of the old advertisements in our files.
Ah, here we are. These used to run in comic books way back when. Perhaps they still do. Sea Monkeys have sold really well over the years.
On the right here is what you actually got, Artemia salina × nyos:
Now Artemia there is actually pretty cool. It's a nifty gimmick and they're truly fascinating organisms in their own right.
The thing is, that from the advertising that you see (and there were some other businesses selling under the Sea Monkeys name that were using advertising that was a good deal less scrupulous than you see above), you might rather have expected something different.
A lot of folks, you see, have been experiencing the so-called 'Avatar blues' in the wake of the film, having been swept up in the beauty and grace of the portrayed environment [which picked up 'Best Drama' at the Golden Globes about 30 seconds ago while I was writing this]. Exactly the sort of strong emotional response that filmmakers seek to instill into their works.
What movie-goers have come to associate with the term 'avatar', however differs substantively from the sort of experience they'd be getting with any virtual environment and its avatars.
Virtual environments can be beautiful, can exhibit grace, and can be immersive and fascinating and useful in all sorts of different ways ... but if you've got the 'Avatar blues', it's like buying Sea Monkeys and getting Artemia salina × nyos.
We don't expect actual user-retention in any virtual environment to rise significantly in the wake of this. We expect that the number of retained Pandora-piners will be about the same percentage as retention for pretty much any other general demographic. Sea Monkeys can be pretty awesome, make no mistake. They just might not be what you really want.
In the meantime, there's a lot of designers across several virtual environments who are making a lot of money copying skins, designs and settings from the film.
[Thanks to DJ Doubledown Tandino for getting us thinking about Sea Monkeys]