Personally, I'm happy to keep paying Dropbox. The Amazon and Google offerings aren't so much commercial products as hegemony extensions. When something's a sideline, I think there's a much higher risk of a mediocre product (e.g., Google Plus) or that eventually gets killed because strategery (e.g., Google Reader).

I'm ok with that for things I don't care too much about losing, but my photos are precious to me, so I'll keep them with a company whose main business is not losing my stuff. Dropbox has one job, and so far they have consistently acted like they know it.