Pros:

  * More choice in terms of technologies you get to work with
  * Less bureaucracy 
  * Once you've launched, typically a very fast life-cycle in terms of conception to production
  * Early on, you can fit the entire company in your brain
  * Investors are less likely to bring in stodgy "babysitters" and just let the founders do their thing

With the exception of the last point, the "Pros" really haven't changed much in the last few decades.

Cons:

  * Limited transparency from founders
  * Weak technical leadership in many "technical cofounders" or CTOs
  * Widening compensation gap versus established companies
  * Equity offers are often poor (related to above point)

For "Cons", the first two have been with us a while. The last two are a recent phenomena as our industry has matured.