I imagine you can set who you are sharing each document with.
Apple have offered online storage for years, these days they call it MobileMe, before that it was called .Mac and before that it was called iTools I think...
Google Docs would improve on that if you were able to edit the spreadsheets and word docs you uploaded using their browser based apps.
I use the MobileMe service and can even access the files form my iPhone. Having said that, MobileMe is pretty expensive at about £70 per year (I think). but of course its more than just online file storage, it synchronises all your computers and phones, gives you web site space, IMAP email and so on. All things you can accomplish using various free services or with paid apps, but of course, it's easy to use...