How long has the top ad space been empty?

It seems every time I come to this fair site, the premium dKos ad space hasn't been taken.  Now, the steep price for said slot is the obvious reason why.  $5000 a week is pretty darn steep.  The regular slots and the second slot usually look full.  Now, far be it from me to criticise Markos' business model, but if that top slot isn't going to show any profit, why not reduce the cost?  

I recently did some comparison with other top blogs.

Eschaton sponsorship (top slot):
$800 a week.

Eschaton is quite a bit smaller than dKos, but not that much.

Talking Points Memo doesn't have their info listed on their page, unfortunately.

On the right, Instapundit, amusingly enough, can't fill its top two places.  

Instapundit Premium: $2000 a week.

Powerline's premium is a mere $400 a week, and it is downhill from there, leading to the tacky muscle ads they sell for next to nothing on the bottom of the page.

Little Green Footballs premium is $750 a week, but it seems to me they could charge more than that (it will soon become the biggest righty blog out there, probably because it actually allows comments).

Which leads me to my final question: how much should Markos charge for that spot?  Is the current price right, or should he knock off a bit because no one seems to be biting?