A topic over at HighRankings named, Expired Domains is where a member asked "I came across a website selling expired domains... what are your thoughts on buying them for the traffic they may still generate?"
The first two or so replies suggest that if the domain name is related to your prior business then it is a worthwhile purchase. The reason being is that you should be able to bring in direct traffic from the old competitors URL and any backlinks will be on topic, so the backlink provider might keep those links and not delete them.
But each expired domain name should be carefully reviewed from a historical perspective. In addition, when purchasing new domain names, it is important to learn if the domain name was ever used in the past. If it was, it might have been penalized by the search engines, you would not want to pass that penalty to your new site, would you?