Google's announcement of Lively, a 3d virtual room product, generated a few "So long Second Life" blog headlines. I'm going to take the contrarian view and claim Lively is actually GOOD for Second Life (SL's own usability issues aside).
Why good? Because it's all about training wheels. Power-user products such as Second Life feed off of consumers who are familiar with similar experiences and hungering for "what next." Second Life's original user base was trained by VRML, The Sims Online, Photoshop, Maya, etc. Basically users who are developing skills or hitting limits in other applications and looking for a place to evolve into.
So Lively can succeed on its own merits by attracting millions of users hungry to get into more immersive chat and expression, and Linden Lab benefits by a % of those users eventually graduating into Second Life, which is likely to be more freeform and open than Lively. And I bet those users are more likely to understand Second Life than folks who are completely new to virutal social environments.
[my bias here is that i work at google - although i had nothing to do with Lively - and was previously an early Second Life team member - so i've managed to dream up a scenario where both win. Of course, if Lively causes some company to want to buy Second Life, that's cool with me too :)]