This is informative and well written. It is true you really do have to mind your domain names. If you let one expire and then be “dropped” from the ICAAN registry, likely some domainer (bulk domain buyer) will pick it up, hoping that it will either make enough $ from being parked or that you’ll be willing to buy it back from them.
Mike Davidson – How to Snatch an Expiring Domain
Also, the process of getting it back (from the article above) sound tricky as you end up bidding against who knows in a blind auction.