I basically agree with Impulses. I use gmail and gcal to run my life. I've got information in Google documents, too. If someone gets access, they may not get my SSN, complete financial account numbers, passwords, etc. But they will get a ton of information about where and with whom I do business, my spending patterns and habits, my contacts, where I will be at specific times, etc. Not to mention whatever I'm thinking and working on. That's too much for someone or some marketer to know. Also, there's the ability for someone to go in and change or delete all that info. If it were read only access, I'd be a lot more comfortable with it.
Of course, I'm sure there are people at Google that can access my entire account if they choose. And anyone that really wants to get in there will do so anyway.
NuevaSync's website didn't really give me the impression of a tightly run, professional, completely above-board outfit. At least not to the level that (I hope) Google is. Fact is, I'll probably succumb in a couple of months if I don't read about any problems from NuevaSync. The functionality is almost too good to pass up.