Millions would be my guess http://dir.yahoo.com/?skw=yahoo+directory This shows 453,000,000 index references who knows how many A Lot
You can get a rough estimate by searching "www" which shows 923,097 results. But there are many sites who don't use "www". So its hard to predict the exact number of listings.
Only commercial sites or other sites wanting express review (7 days) Not true, a backlink from the yahoo directory is very beneficial for the google serps.
No offense but you should really stop making comments on things you have no knowledge of. It is a well known fact that being listed in the Yahoo Directory does help in Google SERPs. You just need to search this forum to see discussions and links from Google themselves on this matter.
Definitely not. Back when the directory was a focus at Yahoo, they had scores of editors who added sites on a daily basis - like a directory that is interested in providing users with valuable resources should. Even now that the directory is no longer a focus at Yahoo they still add sites that are not submitted. Check out a sampling of their What's New from 9/12 - http://dir.yahoo.com/new/20070912/Entertainment/ My guess is that most, if not all, of those listings were added without a review fee.