I use Dropbox, and I (kind of still) think it is a great service, but then I found out that they do server-side encryption, so they have access to all the data. Last Sunday they have tiny security problem which make all accounts accessible using any password.
I have to admit that I do store some important information there, but I did my homework and encrypted it using pgp before uploading. Still, I’m taking the next step: I’ve switched to SpiderOak as my main remote storage/sync service, given that they do client-side encryption, so my data is safe(r). My Dropbox account is going to store anything which I have absolutely problem sharing.