I just recently obtained my 100th feedback rating at eBay, entitling me to the turquoise star! The next star color change won't happen until my 500th positive feedback rating, and that will likely be a long time from now; especially seeing as I registered in 1999 and have now only hit 100.
Surprisingly, I've only recently had my first truly negative experience on eBay. I listed an old hard drive in early December and a person with no feedback won the auction. But I have still not received payment! I plan on placing the drive up for auction again tomorrow night, and will leave the user negative feedback. I'm thinking about adding a requirement that users with less than 10 positive feedback ratings must use PayPal as the payment method. This would prevent situations like I'm in now (where the person wanted to pay via a money order).