What they all said.
Bury your site, to the lowest tier you can fit into.
Consider each word of the full path of the deepest category being an advantage and potential additional keywords that YOU can't put in your HTML.
Write a good title and description without repeating the title or path. The real title of the site.
Describe the site and perhaps some of the features of your site. No keywords or hype.
Example:
Widget World
Manufactures both standard and custom designs. Company history, contact information, newsletter, product gallery and links.
I am a lazy editor.
If I happen to see a good title and description there are three things that come to mind.
1) Wow, someone read the information before they pressed submit!
2) Cool, less work for me!!!
3) Publish.