It went from really shitty infrastructure to somewhat less so to somewhat less so, vs. starting from crap and doing amazing work to make it work well (Facebook), or technical excellence from day one (Google).
OTOH, Twitter is way "cooler" than Dropbox, in terms of having political impact, standing up for users vs. the US Government, used by "cool" (non-tech) people, etc.
Twitter employee here: Always surprised at the amount of ridiculously talented people I work with. :)
To me, it feels like "We have the best people! You don't work here, so you must not be very good. Therefore, I'm better than you."
That's obviously not what they mean, but it strikes chords of jealousy and social exclusion when shouted in a public square.
Twitter has always been known for their Super Ego Employees though. Work 12 hours a day, go home, run twelve miles, cook a gourmet dinner, have three dates (sleep with two of them), check email before bed, sleep for four hours, then start over the next day. (with oversharing online humblebrags every step of the way, obviously)
If you're joining the company today, there better be significant growth story to justify 4x-5x growth from $10 bil baseline. If it's just 2x-3x, heck, joining GOOG, YHOO or AAPL might yield the same results if you timed it right.