I have a mate (Marc Gorton) and thats all he does, He owns a club is selling t-shirts making loads of money. trouble is we never see him hes to busy with his second life, sad aint it.
Second Life is not technically a game - more of a huge virtual showcasing and interactive world. If you've got a big idea then go for it, SL could be a huge help with marketing etc. but if your after fun go play WC3 or if you dont want to lose your entire life in an MMORPG then BF2 / 1942 will suffice.