These little fellas are artifacts of the rite of passage for anyone ascending to the Linden core. Apparently, each new Linden must create a "bear" (literally, a bear) which s/he gives to anyone who asks. I did a quick search while on the call for "linden + Bear" and discovered that there's a whole world of pokemon-like collection and trade going on in one of the many subcultures that litter this digital planet.
From Torley's blog:
The whole "Linden bear" thing dates back awhile, when Nicole Linden brainstormed it and many Lindens ended up participating. Goodwill to Residents via collectible cuteness
I went to a place which was listed as a Linden Bear Museum in Second Life, but it was up for sale as mall property (oh the inevitible march of capitalism through our digital utopia). I found only one place willing to sell - yes, sell - the bears (doesn't this defeat the purpose?) and I took a snap.
I find the collectables culture very interesting. In many ways, this is a representation of the rares-collecting culture in goal-based virtual worlds. Ownership suggests status, of a conceptual closensess to a core. I wonder if there are any linden bears for sale on ebay... ;)