Directories are not too good for say having adsense, ypn, etc on them. Promote, promote and promote again! Go for sponsored links and paid listings. And don't plan on retiring on the earnings! LOL
It can be profitable, if you offer paid listings. You need to have something to offer. Organized categories/Good PR/Cheap Prices/Static Links
just start offering listings for free, build it let it grow untill you have a good PR and then start selling listings... it's a crowded market niche, so it's a lot of hard work