Here’s to betting that a Salesforce.com and Google business partnership has been consummated. Salesforce informs me it will be making an announcement with a “leading Internet company based in the Bay Area” on June 5.

There’s Yahoo in Sunnvale, but my money is on Google in Mountain View. At the Salesforce developer conference last week, CEO Marc Benioff alluded to a report of an alliance in The Wall Street Journal without confirming anything.

I’m curious to see hear what they’ll have to say. Google has always been a bit ambiguous about selling software to businesses, which is what Salesforce does. Adworks, Adsense and search are the crown jewels; its Google Apps feel more like an experiment.

But there’s been a decent level of interest in its software. Google project manager Rajen Sheth recently told me that Google Apps, which went beta last August and was officially announced in February, has about 150,000 subscribers. About 100,000 of those are small businesses, and the remainder a mix of organizations, schools and universities, and large businesses. Proctor & Gamble and General Electric are among the big companies testing Google Apps, he said. Big companies are using a mix in some cases: the free, ad-supported version for some users, and the $50-a-year subscription version, with the ability to turn the ads off, for other users.

Then you have Salesforce, which under the direction of a verbose and media-savvy Benioff, has managed to make SaaS mean something more than what you get from your kindergartener at the dinner table. So you’ve got Google offering very cheap or free online productivity software, and Salesforce selling monthly subscriptions to online business software, and both companies trying to build developer ecosystems around their software platforms. At Salesforce’s conference last week, it previewed an ability to connect its APIs to Google’s to “bidirectionally update Google spreadsheets,” according to a report written by First Albany analyst Mark Murphy.

What could these kids be up to? Stay tuned.