I spent $50 promoting my directory. The traffic was impressive. You can easily get top spot in the sponsored results for niche categories like "gaming directory" etc. I didnt get any conversions, although that may have been due to other issues with the site. If traffic is what you're after, you can get some hits for around $0.50 a guy!
If you are just looking for non converting traffic you can get it a lot cheaper than .50 a pop, but it really is useless. This topic has been covered multiple times, in depth in other threads. Try searching.
Some new stuff thats coming up that i can talk about, as people know we are taking on bid mark 2 or a similar project to a feature in yahoo etc. one thing we will have is when people submit is a free bank of ad word type promotions ( only people listed can use the option and not open to outside advertisement ) it will include 100 listings ( clicks ) on the home page 100 listings ( clicks ) on the directory page 100 listings ( clicks ) main catagory page 100 listings ( clicks ) sub catagory page 100 listings ( clicks ) listings page ( side ) 100 listings ( clicks ) premium , listings page 100 listings ( clicks ) in support pages ( news etc ) giving a total of a guaranteed 700 quick start of 700 clicks through to your site page in the directory. from there you can update or ad to the adverts if you wish, they will be in the form of banner, block, blog, picure or any other form you wish and can even be dediacted and timed with events you are having ie promotions etc. all available soon
Adwords is not good for General Web Directories ,you can better advertise by buying links on other sites
I agree with, the competition on adwords for the term "Web Directory" is really amazing and so the CPC will be really high. So better stay away with it !