Vantaggi
Beer kegs in the kitchen and the relentless "rah-rah" makes you feel like the whole company was your own idea, that you got this "start up" thing right, and that you're all on the cusp of the next revolution in IT.
Svantaggi
You're not on the cusp of the next revolution in IT. You're in another website design, "we can do anything" firm that wants to be cookie cutter. Managers rarely have any domain expertise in the technologies, and most come from big four and have a micro-management bent common among big four. The company does not know how to say no, and is chronically chasing customers that they shouldn't. Managers sometimes have in excess of 10 projects at a time, and then are blamed when things go wrong because they are stretched too thin. Developers are often well over 100% utilized, no bench, and an emerging culture of political intrigue, also common among big four companies.