Once they do this, Google+ for Apps will really finally launch. It will be an extremely strong competitor to Salesforce.com Chatter, Yammer, Asana, and things of that nature, especially if they nail the API.
Among other things:
1) You can do very interesting things with email analytics in terms of discerning the real social network within a business. Gmail's auto-complete already uses a lot of these features to determine which address to show you on each keystroke. They incorporate time into the autocomplete ranking algorithm, as someone you've recently been emailing a lot will always bubble up. Email frequency would be an incredibly strong signal for ranking within a Google+ Apps News Feed.
2) If they nail the API, there's a ton of integration that can be done. Lots of business apps will be built around the Google+ for Apps API. Some basic ideas:
a) Index Gmail and Google Docs to build an internal "person search". That is, type in a keyword like "foo" and you'll find the rank-ordered list of people within your organization that are an expert on foo, whether it be an function name, a client, a project, etc.
b) Seriously buff up Gmail group chat to get a Campfire competitor, with much more persistent group chat history, and far easier collaboration on docs, spreadsheets, etc.
Done right, Google+ for Apps would actually be the final assault on Microsoft's kingdom rather than Facebook's. It would allow new kinds of features that Office would struggle to match.
Id be sending g+ invites for upcoming events and as a side effect reminding people about their g+ accounts.
Instead i have to use facebook.
Then I will be able to swear as much as I like, and upload all of the nude pictures I want, without Google even knowing.
Hell, just make a decent developer API already. The existing read-only one is embarrassing. Third parties will take care of the rest.
Sure, it's a "power user" feature, but don't those drive social sites?
