its limited to 2GB, but you could increase it by installing the app on your phone and enabling the auto upload of pictures. every picture increased it by (iirc) 5MB - and this extra space stayed if you removed the pictures.

haven't used it in ages though.

I know, I have used Dropbox since 2010 ;). But the free tier does not contribute to the revenue of Dropbox. There are no ads (except for Dropbox Pro/Business :p).

Dropbox has some deals with Samsung and others for coupons for certain phones, but most of the 1B is probably brought in by paid subscriptions. Since Dropbox costs $10 per month (plus some Packrat and Advanced Team users), there are roughly 8 million paying users who bring in the revenue. Since Dropbox has ~500 million users, that would be a conversion rate of 1.6%, which seems reasonable.

Of course, I could be way off.