First yes it's good to have a keywork in your domain but a domain should also be easy to remember and spell. eBay doesn't exactly say buying or selling in keywords but it has become to be knows as one due to the brand. hotmail.com makes sense as it uses keywords but google.com doesn't but works as a brand as like eBay it's easy to remember and spell.

About copying names you have to be careful about the keyword your copying. For example cola-merchandise.com would be fine as cola is a general term referred to any dark fizzy drink but pepsi-merchandise.com would be a big no as pepsi is a copyrighted brand.

This is like the problems some sites had with Rapidshare in their name in the past. Rapishare-warez.com is a no but if you had rapiddownload.com or rapid-warez.com it would be ok.