Ah but Slate has Atty's to protect their (and your incorporated) privacy interests. You have no such protection from Google. Google's usage agreement even stipulates they can share that data without notifying you. Only kindof so with Slate - where "reasonable expectations of privacy" apply.
As for Desktop - the software mechanism for uploading your data is already on your machine then. This dramatically increases your risk exposure not only to Google, but also to software that might compromise the Google Desktop (and google is no more nor less secure than anything Redhat, Oracle or Microsoft put out there).
Understand, my 9-5 job is to evaluate, assess and even promote the use of these technologies. Which is why I have more than a passing acquaintance with these issues.
You are putting yourself at pretty significant risk.
For the average person security through obscurity works pretty well. But consider the exampe of Joe Plumber and even Sarah Palin and her yahoo account. Sure you are more careful than Palin. And you are also a more valuable target.