i agree with ithelp. directory submissions do not help. i think link exchange better than directory submission.
It may not help with page rank and stuff like that, but they can be useful by sending traffic your way from people who browse the directories. But I agree with earlier posters that it's not so useful to post to post to all 350, just to the top few.
It depends on the directory. There are some really good quality niche directories that have real targeted traffic. And it's always a good idea to get yourself into DMOZ (although not as important as it once was IMO). With both directories and link exchanges, you just have to be careful about just being lost in the masses, whether it's 10 levels deep in a directory or halfway down a link swap page with 500 other links.