I just wanted to migrate a database from my dev server to my local environment (after having updated from OS X 10.6.8 to 10.9 the other day) and was surprised that the restore on my local machine silently failed. No error message, nothing. First I guessed that this had something to do with permissions in the file system. I checked and everything was fine. So where to look next? Then, after looking closely on the restore form I suddenly saw: "Max file size: 2 MB". Ok, now that explains it. So the OS update had reset some of my local php settings, making it impossible for the backup migrate module to issue a warning of any kind.
There are several issues talking about that in D7 and apparently we have to wait for D8 to hopefully fix this:
The fix is to edit the php.ini and adjust settings for post_max_size and upload_max_filesize. It's dead simple once you know what's the problem.
Those are the kinds of issues that are hard to remember because of their low frequency. And they tend to consume too much time to resolve.
So, next time, I hope to remember having written about before.