According to InformationWeek's Thomas Claburn, "Google is offering these add-ons through the Google Solutions Marketplace, an aggregation point for Google-oriented third-party software and services. It is encouraging third-party developers to build other useful services for Google Apps using Google App Engine."
When I spoke to Google product manager Rishi Chandra, he said the Labs for Apps announcements are part of Google's push to demonstrate that "the notion of three-to-five-year software cycles is over."
Chandra said that Google's immediate priority is to make Google Apps as usable offline as they are online. Long term, however, the company is exploring "how do we make our apps more social. We did something like that with video in Google Video For Business," he added, and Google wants to make a similar transition to social applications for Google Docs.
And even as the company pulls together features in ways that resemble Unified Communications' click-to-call features (recognizing addresses and letting you map them, for example, or adding dates to calendars), Chandra acknowledged that Google is looking into incorporating voice capabilities.
Heck, at this rate, pretty soon you'll be able to run your entire business in Google This and Google That. Duh, I guess that's the point...