DNBolt.com took on a pretty big project and just released their findings. The goal was to look at Namebio reported sales and find which names once sold, were available to register again. There are over 3,900 names.
The post shows how so many sales are one off, one time sales. Some of the names would be hard to resell.
From the blog:
Enough of my ranting. The purpose of this post is to share my discoveries to the passionate domain investing community. I assigned myself a task which was to find ALL Namebio Sold Domains from the begin of time which are now available to re-register. Was this task successfully completed? Affirmative!
You can find the whole list here