The key web 2.0 principle to think about is "harnessing network effects to create products or services that get better the more people use them."
So, for a service business, how might you harness network effects?
1. Make it easier for people to sample or recommend your services. What is the equivalent of viral distribution for software?
2. Help your customers to network. Is there some P2P or social networking angle to what you do? (In this context, see wesabe.com (http://www.wesabe.com) , which aggregates consumer spending behavior to build data about popular merchants, how people like you spend their money, as well as letting people share information about their experience with a product or service, and support each other in reaching financial goals. Could a service like Wesabe be useful to your customers?) [Disclosure: I am an investor in Wesabe.] Let them annotate, review, and share information about your product or service. (Amazon is a great company to study in this regard. They don't have a single big Web 2.0 competitive advantage like Google or EBay -- they just work harder than anyone else to involve their customers in adding value to their product.)
3. Build services that learn from your customers. If your product requires configuration or business rules established, document and export the corner cases so that it's easier for the second customer who encounters the special situation to use your product or service.
4. Read Kathy Sierra's Creating Passionate Users blog (http://headrush.typepad.com>), and apply her insights.
5. Start your own blog, and follow the principle laid out in The ClueTrain Manifesto that "markets are conversations."
Study your own product or service, and think about how networked markets can and should affect it.