Pros
Any startup you work at gives you a whole new insight into how everything works at a company. Therefore, you'll learn so much more just than your own domain. This will help in the longer run of your career. It will also help you understand what the normal benchmark is when you've suffered so much, working for startups. Generally, startups don't suck as much, but this one does.
Cons
Oh, the list is unlimited. For instance, the company hasn't yet grown out of their basement office in Plot 54. There's no proper ventilation, no hygiene, no cleanliness. It's more like a large meeting hall, with no windows. Every time there was an earthquake, we all felt afraid of being found at last if we didn't run out. It was a startup when it started, and it still is! I mean, are you planning to ever grow up? And what's with the unfair working hours? I mean, employees are supposed to be working from 9.30 AM to 11.00 PM, but the CEO is not? Why? Is it the responsibility of only the employees to make your company grow while you lie comfortably in your bed? And all that just because you pay a not-so-handsome salary? Guys, don't join this startup. You're just going to suffer. There's no learning curve because you're supposed to explore everything on your own within the given time and come out with the expected results, otherwise, you're screwed. You're supposed to attend the early morning breakfasts (once in a year, maybe) in early December, no matter how far you live from office.