Though they have been very successful, it's a pity that in my experience they have turned into something of a big co in the way they deal with customers and quite sneakily hide important technical limitations from hackers who might want to use them.
After a year or two of happy premium-paying use, I noticed dropbox was using 100% of my CPU. Some googling suggested this was due to having too many files. Ok, fair enough, perhaps there are technical limitations meaning indexing >300k files is tough (very easy to get to that count if you're keeping open source codebases on DB), so I move files out of dropbox and clear its cache. After a week of constant 24/7 100% CPU usage and dropbox failing to update anything, I contact customer support and get sent copy + pasted boilerplate telling me to do what I've already done.
After more than one email to say 'I've done that, what next?' I get told it's due to symlinks in my dropbox folder. I have several in node_modules folders, and have never had a problem with them before, so I find this weird but remove all symlinks from my dropbox folder. No change after several days.
I try deleting files on the web interface - it refuses to do so for a folder with a large number of files in, and tells me to use the desktop interface (great...)
Also throughout this dropbox repeatedly overwrites work files while I'm working on them (thankfully with backups.)
At this point the customer support tells me how to delete my account if I'm not happy and they simply stop replying to my (polite) emails.
Googling around it appears this issue has existed for at least a year and a half, and yet there is very little mention of it (there's a bulletpoint hidden away on their website) nor does the interface warn you about it at any point. How hard would it be to at least add a notification like 'looks like you're adding a lot of files, please don't add too many more or I might stop working'.
I used to hold up dropbox as a great example of a YC company that was technically innovative and something of a hacker's company, but this experience has left me quite massively disappointed.