A couple KEY things to remember about disputes.
1) Ebay won't hear a claim for an item that you won more than 2 months ago. Period.
2) The minimum amount of the single auction bid must be greater than, IIRC, $25 for Ebay to offer a refund.
3) You can also file a claim with Paypal if you used it. However, their claim period is only 45 days (I got burned on this once). You have to remember Ebay and Paypal have different claim periods. I think there's a $25 surcharge on claims, so if the item is worth less than that it's not worth it.
I've had mostly good experiences buying on Ebay, but a few bad ones. The bad ones, I believe, were caused by the same guy creating different accounts once his feedback got too negative. Because I didn't know the rules at the time, I got burned for some minor cash amounts. Now I always file a dispute at the one month mark, no matter what the seller does/doesn't tell me. That way I'm covered if it doesn't arrive. Just be sure to end the dispute if you receive the item.
Ebay doesn't have the greatest reputation when it comes to resolving disputes. In fact, google it and you'll find Ebay actually has a pretty bad reputation when it comes to dealing with bad buyers/sellers. Someone will screw you and then keep right on selling without any apparent action from Ebay (everything is handled confidentially, they say).
The great thing about Ebay is that so much is available and the process is so simple. That's what makes it great. Were there some legitimate competition, Ebay would be hurting.