I have bought loads of stuff off ebay over the years, including my 20D and a 100-400L lens. I have had a couple of deals where things weren't 100% as expected (not the camera or the lens, they are both great) but out of over a thousand purchases that isn't a bad record. The little bit of money lost on those deals has been saved many, many times over on all the rest of the stuff I have bought.
I am a big ebay fan, but you do have to be careful. Read the descriptions carefully, only buy expensive items from people with lots of quality feedback and a high positive rating, pay by paypal and fund it from a credit card (then you have protection from paypal and if that fails you can take it up with your card provider and claim from them).
DON'T buy from anybody new who is suddenly offering lots of high dollar items (particularly if they are 'buy-it-now' at very low prices), don't pay by Western Union and don't buy from somebody who won't agree to let you pick an item up in person. You don't actually have to go and get it, but asking if you can is often a safety net. If they say no it could be because they don't actually have the item.
Use a bit of common sense and it is very safe to buy from ebay, the vast majority of the scams are blindingly obvious.
My verdict would be 'good'. I base that on my experiences buying over a thousand items, and selling about five thousand, over the nine years I have been using ebay.