There's been a good amount of buzz in recent months about whether Salesforce.com is prepping itself for a marriage of some sort. What about Salesforce.com and Workday? The two could make one heck of a SaaS powerhouse.Both are doing a good job of moving their software services beyond the small business market and into large companies, yet they don't compete with one another. In fact, Salesforce.com said today that it was selecting Workday for human capital management. In a statement, Workday CEO and founder Dave Duffield (who also founded PeopleSoft) said," We look forward to continuing our close collaboration with [Salesforce CEO] Marc [Benioff] and his team, both as a customer and a partner... ."

Benioff remarked in a statement that "Workday's rapid ascension to on-demand HR leadership is an outstanding example of the dramatic industry shift to software-as-a-service for mission critical enterprise solutions."

Not sure I'd call it a leadership position just yet, but Workday is becoming a company worth paying attention to. I just learned today that it signed its biggest customer yet: electronic maker Flextronics is using its human-capital management system to serve 200,000 employees in the U.S. and China. Last September, Workday signed on Chiquita Brands for 26,000 employees using on-demand HCM. Other big customers include 18,000 users at Life Time Fitness and 16,000 at ITT Defense.

The company, which ended last year with 15 customers, now has more than 40. Of those, eight are PeopleSoft and/or Oracle replacements. Workday's payroll and financial on-demand software is newer and growing much more slowly, still mostly focused on smaller business customers.

Workday is still small potatoes compared with Salesforce.com, which is approaching $1 billion in annual revenue after nine years of business. But I could see Workday's human-capital management alone on a similar growth track. On-demand financials, I'm not so sure, but Workday execs are convinced even larger companies will get more used to the idea once they become comfortable with HCM.

Yes, I think Workday and Salesforce will be strong partners for many years to come. And in the quickly consolidating software industry, it's not hard to imagine that relationship forming into a happy legal union.