If you have good ranking for your keywords in yahoo already I would say dont bother, if you dont then its something which can help improve you ranking assuming the editor accepts your site.
It also depends on another 10 billion factors. If you sell customer made piano's and are the leader in your niche with a minimum sales value of 50K it's probably worth it. If you specialize in the sales of empty crisps bags which you sell for $0.01, you;ll need a lot more customer to get yout well-deserved ROI.
Don't buy it to improve your ranking... that would be a waste of money. Only buy it if it will drive traffic directly from the listing.
I have 3 websites listed in yahoo directory and get less than 5 visitors a month combined, how does everyone do?
I just signed up a week ago. I haven't checked how many visitors I've gotten but I know I've had 4 conversions. Still... $299 does seem a little much. I think most industries wouldn't break even.
If you spend more then $1000 a month on Overture PPC, spend this $299, else not. Do you have lots of top10 rankings in Yahoo ? If yes, but it. If not, don;t.
I've heard of rare occasions where companies will purchase a listing simply to get spidered quickly. To reiterate what everyone has said - it really depends on your budget and industry.
Be careful with Yahoo's directory, there is a very interesting thread about this at seochat. Seems that getting listed in the directory can get your title changed, and your SERPs drop like a rock http://forums.seochat.com/showthread.php?t=39292
I read that a few days ago, but the way I see it... if I'm banned already I don't have much to worry about. lol Certainly, if I wasn't banned it would be a serious consideration.