Juat A First Hand View
I thought some comments from an individual like myself who is actively working with second life might be valuable to some.
I spend time working with a small core team (3) in Second Life. We are using it as a platform for bringing together an art community via 3D internet. I am not unbiased, however I am interested 3D internet technologies as a whole and don't feel overly biased towards Second Life specifically.
Having watched, experienced, and interacted in this media since 2006, this is what I see.
1. Bots are now a ToS violation in SL, leading to improved performance and reduced "fake" traffic. Yay!
2. Even with that change in policy, the average number of users is significantly larger these days. I often see 65,000+ or more people logged in at one time.
3. From my point of view there is ample activity in Second Life including live music, live opera, live theater, clubs, "chat room events" of various sorts, tours, museums, art galleries, building events, discussions, movie nights, etc...
4. Every single day 125 to 200 people come to and visit my Art Gallery... that is several thousand people a month! Personally, things seem to be buzzing!
I do not think that Second Life is primed and ready to replace the 2D internet or Facebook; not yet... But someday, not too far from today, a technology like Second Life will in my opinion make this leap. Linden Labs just happens to be the front runner today with their Second Life platform.
Hope it helps!
Second Life SIM: http://slurl.omni.fm