.Biz is a gTLD that is going to grow old gracefully. It's kind of like the dot org gTLD back in 1997. They were the ugliest things to look at or pronounce. The ".org" name didn't roll off the tongue. No one referred to organizations as ".org's". Over the years, they have been advertised more, and have gained a sense of "belonging" in the domain community. A trusted brand if you will. The same will happen to biz. Only certain ones however will attain limited type in value (example:
www.Microsoft.biz,
www.Ibm.biz). Even dot org names do not have the type in value of a .com.
One thing to note. It is the generation being born right now that will decide the future of domain naming. They will be the ones who will grow up in a world with many TLD choices. My guess is the TLDs that get advertised the most will get noticed. All businesses and/or industries have to advertise. It's their lifeblood. My bet is .com will still be around in 20 years. Will it be king? Not if they continue to use the domains as PPC pages!
One thing to note: Toolbar technology is going to make things interesting. Instead of making your site SE friendly, we'll be talking about how to make our site "toolbar friendly"--lol!!