Are the cheap Lith-Ion Batteries sold on Ebay any good?

Was wondering if those cheap Lithium-Ion batteries they sell on Ebay are any good. I purchased two for my previous DSLR but never used them, they were back ups and I didn't need to use them. Bought a new DSLR Sunday and would like to get a couple of spare batteries but I don't want to pay $75 a piece for them. They have the 3rd party (Chinese made I assume) batteries on Ebay for around 12 bucks each. I know that if something happens to my camera while using them might void the warranty, that is not an issue. I can get about 400 shots in RAW format with the Nikon batteries, so even if I could only get 200 shots from one of the third party batteries that would be good. Interested in responses.

The Chinese batteries don't seem to have the capacity of the OE batteries. I ordered 3 for my Canon point and shoot, and 2 more batteries for my Motorola Droid phone. I would estimate the capacity as about half of the original equipment battery, even though the rating marked on the Chinese batteries is greater. The batteries are a ridiculous low price, so I don't feel too bad.