If I was the founder (or co-founder) of popular websites, such as: Youtube, MySpace, Ebay, Amazon.com, Napster, Wikipedia, etc. and I was offered a BIG sum of money to sell, I would ask:
"Cash, or check?"
As you mentioned, Google bought Youtube for over 1 billion. Anyone who would turn that offer down, would of course, be a total (to put it in nice words) "idiot".
Even if took me many years of blood, sweat and tears to get a company started, that would be a great "pay-off" (retirement) to a successful, entrepreneur "career", for sure=)
I would be like someone at the NYSE, yelling: "SELL! SELL!"
In one way, I wouldn't care what happens to my company, when it's out of my hands...
In another way, I would also have to say that I would like to sell my company to someone that I know won't destroy its "integrity." Surely, if your start-up company is successful and if you're giving it away, you must be proud of your accomplishment and care to give it a good, new home.
However, there's also the possibility that I could start-up a company and maybe cared for it so much, I might NEVER sell it...well, if it was a 1 billion dollar offer, I might re-consider=) More than likely, I'll probably just sell the company anyway and enjoy my "vacation."