Hey, how does a domainer keep from over-submitting to search engines/know when to quit? Is it necessary to submit at all [maybe even better to abstain?]
Its best to not overdo it, using mass submit search tools will hurt your ranking. If you do it by hand and do not submit more than once to the same directory/search engine after you have been listed, you should be fine
If you are looking to submit your website then make sure that you are not submitting your website over and over again to G. The search engines have stated that directly submitting a website will take time to get indexed and thus it is better to submit your website's sitemap in G.
It's really not necessary to even submit your site if you can get a couple links from URLs on other sites that are already indexed. I prefer to let Google and the other engines discover my sites naturally. IMO submitting XML sitemaps is totally unnecessary unless you 1) are trying to get your site indexed but have no backlinks (in which case it's not going to rank anyway so why bother) or 2) you have a huge site w/ hundreds of thousands or millions of URLs. Sites with hundreds or a few thousand pages really don't need sitemap.xml files. Your linking structure should be enough for the crawlers to prioritize which pages should be indexed first. If it's not than you have information architectural issues that need to be addressed.
It's not necessary to submit your sites. If a search engine cannot find a good site (sitemap, unique content, proper optimization, quality links) on its own then you probably don't need it.