There was an article in the Boston Globe today (June 12), on customer service delivered via instant messaging. There are some interesting uses going beyond simple "Click here to talk to a rep..." For instance, they cite Lands End as popping up a message as soon as you enter the site - kind of the equivalent to a greeter at the store, I guess. Or another company, Proficient, provides profiling services so they can route you to a person based on location and the content you are looking at on the page.
Article: Instance Results
Note: I have no idea what technology is behind these web sites, and the Globe does not say either.
Another good use for Sametime - Customer Service