I've always been very cautious about recommending companies to go into Second Life, although my occasional public performances on the subject may indicate something else. And now that Second Life has been declared dead by the media just as quick as they made it a hype ... I have a contrary view again.
But rather then explaining my point of view, I'm going to send you off to Neville Hobson's blog who has perfectly summarized the current status of Second Live.
Thanks Neville, no other sources needed :)