Service-as-a-software (Saas) company Marketo is riding the trend of real-time analysis of customer behavior, making it one of the fastest enterprise software companies in the venture market and a solid IPO prospect for 2011.

The company, a startup founded in 2006, recently surpassed 600 customers in July. Marketo’s revenue is approaching the $20 million level, based on estimates from company sources that the average annual sales per customer is in the $30,000 rage. While the company is not yet profitable, it looks to be a solid IPO candidate for later in 2011 or 2012.

What does Marketo do? Quite simply, it helps you track and optimize your customers – and your potential customers. Built to tightly integrate with Salesforce.com, Marketo aggregates publicly accessible online data and meshes that with information in a company’s sales-force automation database. The company’s software than calculates potential ROI on customers as well as identifying “hot leads” for the sales force and managing leads through the sales process.

"Using Marketo helps our sales and marketing teams understand specific call to actions that MobileIron prospects are responding to over time ,” said Adam Stein, Marketing Director at Marketo customer MobileIron.  “Additionally, we leverage Marketo to automate and personalize our outbound sales and marketing campaigns."

One big advantage with Marketo, according to Stein and other customers, is that it can be “instantly” integrated with the Salesforce.com CRM tool. For example, because Marketo is sold as a SaaS product, the customer needs to only sign up and give Marketo the subscription information, while Salesforce gets automatically integrated on the back-end “in the cloud,” with no installation required at customer sites.

In April, the company raised Series D funding of $10 million, bringing its total funding to $32 million. The Series D round was led by the Mayfield Fund, with participation from InterWest Partners and Storm Ventures.

Marketo’s major competitor is Eloqua .  Salesforce.com could also be considered a competitor if it develops features similar to Marketo’s. But given Marketo’s strategy of integrating with Salesforce, it’s more likely that Salesforce will end up buying  them.