Trust: The Achilles heel of SaaS

I guarantee you that every time someone decides to use a Software as a Service (SaaS) solution for their company, there's a specific thought that runs through their heads:
Can I trust this service with my confidential data?
This is a legitimate concern. When you use a SaaS solution, you're basically making your company an open book to that service. When I took Yammer for a test drive the other day and scribbled my thoughts about it, a few people told me I was a little harsh on them. My concerns with it were primarily around trust and how ready it is for a mid-to-large enterprise. I love the concept, I've been pushing for it ever since I started using Twitter. But, that doesn't give companies aiming at enterprise users a free pass. But that did get me thinking about the concept of Trust and how it relates to SaaS.
I don't think this is a simple issue. You probably don't care if people outside the company see SOME data, like what type of sandwich was served at the team lunch. Talking about what you had for lunch on Yammer is fine. But what about HR data? Or M&A data? Certainly you don't want employees talking about a potential acquisition on Yammer, because you ultimately don't know who has access to it and there are legal implications to people seeing it.
There's a certain amount of trust being a well-known brand automatically gets for you. That trust can help you get over this "trust objection" and close the sale. Yammer will probably not be trusted to host Cisco's data, but I would venture a guess that Yammer would not have a problem entrusting its data to Cisco. It's one of the few advantages of being big that small startups just can't overcome.
This also raises an interesting question: which companies have the kind of inherent trust in their brand that they could leverage to launch a service like Yammer and be successful with it? My short list includes Microsoft, Salesforce.com, Cisco, Amazon, IBM, and MAYBE Google. On the polar opposite end of the spectrum you have startups and AOL (who has a habit of disclosing confidential customer data).
Which companies would you trust with your confidential Twitter traffic?



