Adding a description when you are offering a domain name for sale is something that takes time. Your description should be specific about the exact domain and it really should be a quick and to the point sales pitch.
I admit that I have very few descriptions on most of my domain names for sale. I need to change this but I was just motivated to do it quicker!
I have Yoxa.com listed at Afternic.com (which I just lowered the buy it now to $1,500 if you are interested) and I often do a Google search for domain names that I own using the exact matching term(s) to see if I run across any news stories or just discover anything interesting.
Today was one of those days that I discovered something interesting!

My description is being used as the Meta Description for a page that is indexed # 3 for the matching term yoxa on Google.com .
A.) this is nice to see that Afternic domain listing pages are getting indexed
B.) it is nice to see the description being used as the meta description
The one bad thing about B, is that I was not aware that this happened! I do not recall ever seeing anybody write about it, nor do I recall ever hearing it from Afternic.
Now you have if you had not.
In general, it is not a bad idea to have some "sales pitch" in a description area on Sedo or Afternic. You can also have a page for your specific domain on your own sales site. I even set up a mini-site like HandTrowel.com from time to time. The little mini-site for HandTrowel.com does two things! It allows visitors to know the domain is for sale via your pitch and secondly, it get’s indexed (likely). In my case, HandTrowel.com currently ranks # 3 on Google for the term hand trowel .

I make sure to use my meta description with any mini-site to let the reader know the domain is for sale and how it can help them. Doing so in the title also doesn’t hurt.
If you find some extra time, try adding some text to your empty description boxes. I would start at Afternic if you have domains listed because I can now tell you that the description is used for the meta description if your domain listing page gets indexed. You can catch a buyers eye without them even needing to "click" to see your sales pitch!


Eon
Good tips Jamie! And nice surprise those sales pitch get indexed.
One week ago, I begin my experiment adding separate (and moderate) name-for-sale pages to my mini sites listed for sale or auction, where I give some descriptions appealing to end users, Google search snapshot, Domain/site stats, Estibot appraisal links, and the auction entry link. I will see what will happen in 1 or 2 months.