Greg Verdino has an interesting post on which brands on Second Life are doing well and why. BigPond, Pontiac, IBM and Showtime have great "dwell" or traffic on Second Life, but BMW, AOL, American Apparel and Starwood do not.
That's surprising--unless you think of community. Those brands that build community, get the avatars who want to hang out. Those that do one-offs, or try to simply sell product, do not.
According to Greg, IBM is successful because it uses Second Life to promote interaction within its own corporate community (employees, customers, business partners) regardless of geographic and organizational boundaries. IBM also uses SL to "engage in-world builders and scripters through their more recently launched IBM Codestation, which serves as a forum where users can access shared resident-created chunks of code." Greg says IBM's "dwell measure eclipses that of technology competitors Dell, Sun, Cisco and Intel-- all of whom seem more focused on using SL as a platform to promote products and services."
To succeed in SL, as with blogs and all social media, build community.