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Would anyone say the benefit of these sites is from the traffic they generate in and of themselves, but not to be found in SEO?
On a slight tangent, does being listed in the Yahoo Directory help with listings in Yahoo's natural searches? (I only just came up with this question, so I'll go take a peek at the Yahoo side of things and see if it's been posted in there.)
Yahoo! is a directory worth being in, as it clearly has some 'authority'.
But with most directories, you'll find as much value in a free directory as in a paid listing; indeed, I could name scores of 'paid for' directories that are an utter waste of cash, and many 'free' directories that are very good places to be.
When selecting a directory, always start with the free ones, then the paid-for 'niche' directories for your topic, finally the 'paid for' general directories.
'paid for' means either a one-off payment for a permanent listing, or an annual payment: think long and hard before committing to an annual payment; you'll find it very, very rarely value for money.
There are way over 100,000 general directories. Probably fewer than 300 of them are worth submitting to. Be fussy; why make an idiot rich? ;)