These videos are certainly funny, particularly the iPhone vs HTC one that was popular a few months ago. But as cscotta pointed out there's an interesting trend of picking certain flaws in particular databases and highlighting them without telling the whole story.

Anyone watching this might believe that MongoDB has a major flaw where data isn't written immediately and you have no idea if it has successfully been stored to disk. Whilst it's true that inserts are not immediately written by default, you can a) change the startup config to set the delay time b) force a write of all pending changes from the command line c) force the write from your call to the insert/update/remove/etc method in all the libraries and most importantly, d) request the library method wait and return the response from MongoDB so you can determine if the write was successful or not.

This means you have complete control over when you need fast inserts at the expense of potential data loss, or when you need to be certain the data has been written.