My wife and I just left Dropbox, because paying $20/month for 200 GB of storage (which she just exceeded with our photos from before kids as well as our kids) is crazier than paying $10 for 1 TB of storage. The only feature I miss is the ability to auto-backup our photos to our online storage - Google does some kind of backup to Google+, but that's worthless to me. Dropbox would auto-upload my pictures to a folder, which I really liked. Oh, and IFTTT doesn't seem to work well for us for backing up the photos, seems to take forever and requires tweaking, Dropbox's system Just Worked.
I understand Dropbox is coming out with some email client, ok, yay, Yet Another Email Client. That is so old and tired. Do something innovative. Now, all this said, if there was an EASY way for me to have Dropbox-like functionality against an S3 endpoint where *I*/AWS runs the box, I'd be game. The options out there suck for users and honestly aren't great for power users either.