There is a thread at DigitalPoint forums from back in April that caught my attention. The thread is named Google "ADD URL" hurts your potential rankings? which links to an SEO Chat article which reads:
First, let me tell you what you don't do. You don't use the "Add URL" form with Google at http://www.google.com/addurl.html. Believe it or not, using that form to let Google know about your site will actually hurt your PR and, at the same time, make Google rank you lower. In other words, you absolutely never want to use that form, or the similar form on any other search engine, to promote your website.
The thread at DigitalPoint takes issue with this quote. If it was the case that using the Add URL form at Google (or any other search engine) would hurt your rankings, why wouldn't a competitor submit all your sites time and time again? What I believe the author was trying to convey, which he did not do, was that one should not waste their time with automatic submission programs. The author, in my opinion, should not have gone to the extent of writing - "Believe it or not, using that form to let Google know about your site will actually hurt your PR and, at the same time, make Google rank you lower."
On topic to this, is a recent thread at Search Engine Watch Forums named Whats a good program to do the once-a-month submissions?