I will consider socialbookmarking as my top priority, after that directory submission is just a nice supplement for me I will not expect much from directory, but for long term it could help improving your website seo.
As was said earlier, It is one step in an overall link campaign. Keep Building links and good things will happen.
A good directory should raise your pagerank. A good homepage bid directory link will also raise pagerank
You Submit Your Site in any PR Directory. You Submit Like 4000 Directory 3,4 Months Your PR is 2 or 1
If you submit to a couple hundred general junk directories your page rank will go up. Probably to about a page rank 2. The thing is that general junk directories won't significantly help you rank better in the search engines. If you want to rank you need backlinks from quality resources. For example, a listing in a quality directory such as botw.org will help you rank better in the search engines.