Last year the story broke about very questionable tactics of Dropbox Mac to gain root access.
This year I had a client whose machine was crippled because of a fun Dropbox default where, upon inserting any USB device Dropbox will automatically copy. The user inserted a camera with 4GB of hunting pics and it basically downed his machine. Now maybe he clicked on something to technically approve of this. But I surveyed the user base whom I had asked to install Dropbox and more than one had experienced a problem with this "feature". In one case the employee almost got in trouble for personal use of a machine, because she had connected her phone and didn't realize all her personal pictures were copied there. Less savvy users were involved, but I need to feel comfortable recommending a product like this to less savvy users.