I occasionally hang out at a couple of dedicated domaining forums and look at their marketplaces - for sale, wanted, etc. I can never understand what their criteria are for listing domains for sale as being "premium" domains.
Sure, a short, generic word on the .com is likely to be valuable. Even some EMDs on the .net or .org could have value, especially if you're chasing AdSense and have done your research on the high value keywords. But I simply can't understand why gobbedlygookblooklook . info or something like that can be a premium domain.
Maybe I just don't 'get' it, or maybe the domaining forums aren't particularly fussy about what they'll list as a premium domain.
If we have any experienced domainers here, please tell us how you would classify a premium domain.