I began manually submitting a new site about 2 weeks ago and have been keeping an eye out for visiting spiders. The site has not yet been submitted to any of the directories and had zero links pointing to it.
I noticed that none of the engines I submitted to were crawling the site and a few days ago people in the forums gave the 'heads up' that they were noticing several spiders crawling their sites.
We have several separate sites that are related to each other and yesterday I added a few links from some of these sites pointing to the new site. This morning I see that googlebot, fast and the Teoma/direct hit spiders have been in...
I know its not very scientific, but based on this would say that to get spiders to index a new site - one needs to get links.