Update below: Phil Wainewright raises an interesting beef in his post on SaaS data worries. In a nutshell, Phil says it's strange that people are trotting out the "your data may not be safe" argument when talking about Google Office.
Phil then notes how it's an argument against SaaS.
I wouldn't go that far. Here's why: When it comes to Google there's a perception difference when it comes to Google Office vs. other players like Salesforce.com. I trust the latter more with my data. Why? It comes down to focus.
Google Office is a side venture at best. While Google is quite capable I'd be reluctant to put all my data there. If Google loses my data there's no downside for them. If Salesforce or NetSuite blow it, there business will tank quickly. The reputation hit matters.
Another thing at work here may be that Google is getting too big. I'm not sure folks would host all of their data with Microsoft either. Anyone who has watched hosted data disappear--I have 100s of columns that have gone extinct when a Web site disappeared--picks their data keeper carefully.
Update: Phil Wainewright has another interesting post--he's full of them btw. He notes, like Rob Hyndman, that if Google lost data it would hurt its brand so you're data is likely to be safe. I don't disagree, but as an enterprise--which is my perspective--I want someone with a core competency in SaaS. I liken it to going best of breed--Salesforce and NetSuite are best of breed and Google is a SaaS rookie at this point. And as a customer, I just think it makes sense to go with a company that specializes in SaaS and is proven. Let's face it, Google is an advertising company. Perhaps Google becomes known as a SaaS company, but I'd be a slow follower here. Personally, I reckon Google Office is a distraction tactic to keep Microsoft off search.
Phil also asks whether my logic applies to Microsoft and others. The answer: Sure it does. Microsoft is trying to sell you shrink-wrapped boxes of software and it'll protect that business. Therefore, Microsoft is going to half step on the SaaS. Perhaps, it's just a game of perception, but it's there. Ditto for SAP.