Furthermore read onward for some examples from Zemanta itself, which afaik is a startup.
I could also get into the experience I had when using Google App Engine for my startup a few years ago. Horribly over-engineered architecture, nothing worked, had a whole bunch of trouble and everything went all manner of bad to worse very quickly.
But hey, we had awesome scalability! Until we got 200 users and everything started falling apart because of the overhead of keeping all the different parts of the system communicating.
PS: the "saving is taking too long" example is actually aimed at Buffer not Twitter or Google :)
Furthermore, Google and Twitter aren't startups.