Apart from .com, which has the advantage of being the "go to" tld, (on more than one level), and .net and .org, which both have the advantage of recognizability/familiarity because they were next in line, keywords are keywords. A .biz site is built in the same manner as a .com site and doesn't resolve any slower on the www or offer any less features than domains w/ other exts. I have, yet, to see any solid proof showing that search engines give one tld preferential treatment over another. SEO procedures are the same- there are no special rules for site submission or meta-tags usage that would differentiate one tld from another. From the POV of the namespace, the www is the land of equal oppurtunity. Until ICANN takes the unprecedented step of removing a gtld from the worldwide web, .biz is alive, IMHO.
The condition of any namespace, including .biz, is in the eyes of the beholder. What is the business model that is influencing and shaping the registrant's vision for the domain? What was the purpose behind registering the domain? If the name is for development, a .com name has promotion advantages that a .biz or a non-.com name doesn't have. (ie it is the tld that SE's default to.) But at what price? Is the developer a sweat equity, "do-it-yourselfer", or does he take more of the "turn-key - throw some money at it", approach? If the intent is to sell the name in the aftermarket, what are the time parameters? Is the plan to have a quick turnaround sale or is the intent to register a name as a long term investment, that will, (or may), pay off, in the future? What is the acceptable level of risk for the investment and how many years of renewal fees does the name justify?
Ultimately, the state of the .biz, (.any), namespace is a matter of the domain name reseller's and/or developer's intent and selective perception. The success of the domain and the website that it represents depends upon, in no small part, the skill and work ethic of the registrant. The TLD, itself, helps organize and expand the web and does so w/ complete neutrality.