One of the first things I thought about when I decided to start this process of moving files to Dropbox was the amount of time it takes to upload a large volume of files. If you use Mozy or one of the other online backup services, you know how long that initial load of a high volume of data can take. I wanted to avoid having the laptop constantly transferring files for days so I moved blocks of data that would only take an hour or two to upload. This probably resulted in the entire project taking more days to complete but it allowed me to work on the reorg for short periods of time and to not feel like the it was running my life.
Along that same line, all of this data had to be downloaded to the other computers I set up. I made sure those devices were turned on whenever I was moving files so they could keep up.
There are free Dropbox apps for smart phones so I now have access to my files from my Android phone. The phone app does not automatically download all of the files to your phone like it does to computers so there is no worry about the available space on your phone. My experience with the Android app is that you can look at jpgs from Dropbox but when you open a PDF, Word or Excel doc that file will be saved to your phone. You will need to delete those once you are finished if you don't want them to remain on the phone.
One thing I decided not to move to Dropbox is my digital photo collection. If I did that I would need to upgrade to the 100 GB plan for an additional $100 per year and I wouldn't have very much room for growth before that would be maxed out. I have been using Mozy as my online backup service and will continue to use it for photos, my email (since I don't think it will work properly from a different folder) and a few other files where the program seems to want them in a specific location. Two years of Mozy costs $103.95 so that's cheaper than upgrading to the next level of Dropbox and I won't run out of space.
Oh and since I am keeping Mozy and it's unlimited, my Dropbox folder also gets backed up there so my genealogy files are doubly backed up to the cloud.
Disclaimer: I have no affiliation with Mozy or Dropbox. However, if you click on the Dropbox link and sign up for an account, I will get some free space (500 MB) added to my Dropbox account but so will you (250 MB).