Hi fellow webmasters, during the last two years, I've been registering long-ago expired or deleted domain names that I liked, and I really saw no problem with it; recently though, a relative asked me what would happen if the previous owner of that domain would claim it back... Honestly, I told them that domains are owned until they let them expire or delete them, and after that the domains won't belong to them anymore. What's your opinion? Could someone really come and claim a domain back when it hadn't been re-registered for years?
The only way they could is if the name is a trademark, all others are fair game. Basically you are renting the domain name anyways, so as long as you pay the rent, you can use it.
Just be careful of trade marks, and don't try to find the old owners and offer it back to them for a price.