Premium Domain names are domains that are already registered, but are available for sale at a higher price. Sometimes it will be an individual selling the domain, or it could be the domain registry (Like Donuts Inc. or Radix) selling their top quality inventory at a higher price point. These domains can be priced anywhere from a couple extra bucks to millions, depending on the domain name, the level of interest, or the amount of traffic it organically receives.
Alternatively, you can monitor a domain name for free at a number of locations. DomainTools.com offers a free domain name monitor tool, as does DomainHole.com (both available with free member registration). Once you receive an email notification that a domain has changed status from active to expired, you can follow the process listed above to enter a bid at the auction partner site.
Everybody going to start using old domains should also know how to get them, I'm going to post soon article about it on seomoz as there are several ways starting from online rankings and lists up to dedicated seo tools that you can run on your computer and get precise and actual data on demand for any domains lists. Anybody intersting in such tools please visit our website: http://en.exdomain.eu/
If you buy a domain from a 3rd party, the backlinks are valuable. I always wait a few months before redirecting, so just set up a quick minisite until two page rank updates have passed and then go ahead and 301 redirect. However, it seems that you'll get the link juice from the back links, the anchor text is ignored by Google. Buying a domain at Godaddy TDName expired auctions, seem to not count as a dropped domain if you immediately set up a mini-site.