submitting?

[kosar]

for a site that has been existing for about 7 years. how often should submit to the major engines?

[pleeker]

If you're already listed in the major search engines, never.

If you're not already listed in the major search engines, never.

Search engines will find your site more quickly when they find a site that has a link to yours. Get other sites to link to you.

Submitting to web directories is something completely different, and if you're not in directories, you should try to get listed. Follow the rules and guidelines at each directory WRT how to submit, when and if to resubmit if your first try didn't work, etc.