Taking advantage of a variety of freebies offered by dropbox, I increased my space from the base 2GB to 5.8GB. I'm also working on a potential 1GB increase by two referrals. If they sign up, each party gets 500MB extra.
1) Uploaded photos via the Camera Upload feature in the IOS app: each 500mb photo upload scored 500MB increase. You must do this with an app in IOS or Android to get the space. You can't just copy photos over to your Camera Uploads folder on a computer. So, the process is slow.
2GB increase to 4.5GB.
2) Completed 5 of the steps indicated in the "Getting Started" guide on the desktop dropbox web site. This gives you another 250 MB. This one was kind of a surprise. I had already done 5 steps by the time I looked into it, just had to hit the option.
3) Downloaded the Mailbox app for IOS (sorry, no Android app yet) and linked it to dropbox. Earned 1GB. After I earned the extra 1GB, I just deleted the app. Still have the space.
Total earned: 3.75GB.
The reason I got started on this was because I had been pretty bummed that Picasa was getting unusable and the upgrade path was google+.
So, I did some googling around about photo sharing apps. Surprise, several reviews and postings recommended dropbox as the easiest, cleanest way to share photos. I tried this out from the IOS 7 App. When I examined it, I liked what I saw.