It was due to expire in Dec 2008 and I had no intention of renewing it. Then out of the blue, I was approached by a domain broker. He asked me what I wanted for that domain. My initial thought was just $50 but then I asked him to make a suggestion instead. He then just suggested $950 and I took his offer immediately.
I was completely lost as to why that domain was worth that much. It is only after that the domain had been transferred that I knew the reason. Let's say a domain such as uknet.net or usanet.net would be worth some money. It turns out that slo stands for Slovenia! Now it seems that the price I sold it for may have been rather low!
The moral of the story is that think carefully before you let your domains expire. There just may be something in that domain that is not apparent to you! Also if you want to buy a domain, approach the owner directly and not through a broker. Or else you may end up paying much more for it!