I worked for a company matching that description precisely, and can attest to the fact that it really sucked, a lot. The strange thing for me was that it was a subtle shift from "wow, this is so exciting" to "I can't believe how much this sucks". I can't even pinpoint exactly when it happened.
In the beginning it was exciting. Lot's of money floating around, everyone assuming things would be wildly successful and we'd all be rich. Reality was a hard pill to swallow (I was the fifth employee of a company that grew to just over 100 then contracted to around 25). That said, I'm not really tempted to go to the corporate world. I can't just unplug my ambition and accept being a small cog in a giant machine. I would much rather take all the lessons I've learned on "what not to do" and channel that into a new (and hopefully better) startup.