Up until around five years ago, I ran my own personal mail server. If you sent an email to me, it arrived at a server that I owned and maintained. It was fun, but I became too lazy to continue maintaining the server, so I migrated to Gmail. Recently, however, I've kicked around the idea of going back to running my own mail server. Reasons range from keeping my SMTP and IMAP knowledge in check, to simply not wanting a copy of my mail on Google's servers.
That latter reason, though, might be completely moot.
I was catching up on my RSS feeds last weekend and came across a blog post titled, "Google Has Most of My Email Because It Has All of Yours". It highlighted a very real effect that cloud services (in this case, Gmail) can have on people who don't even use such services.
Now, it's no big revelation that if you use services such as Gmail for your email, or Flickr to store your photos, then you are allowing them to have a full copy of your data (at least I hope it's not a revelation). But the collection of data belonging to secondary (or even tertiary) users of the service is something rarely discussed. And with the proliferation of SaaS and hosted services, this collection will only become larger.
I don't want to advocate the full stop of using hosted services ' that's unrealistic and irrational. But I do want people to become more mindful of this in the future: The next time you're filling out a sign-up form, take 10 seconds to think about how other people might be impacted by your use of the service.