Myths about Search Engine Registration
Many people expect to instantly get a lot more hits after registering their site. This will not happen, and anyone who promises such results is what James (my 8 year-old) colorfully refers to as a "silly peanut-butter" (in other words, a liar).
Registering your site will get you more hits, but it will take weeks or months for the increased traffic to become noticeable. After you register your site with a particular search engine or index, it can take anything from 5 seconds to 5 months for them to actually list you, if in fact they actually do. Registering at a particular index doesn't guarantee that you'll actually be listed; many indexes are very selective and only list a small percentage of the submissions they get. And the major search engines? Well, they're all taking months to add new listings. Furthermore, just because you are listed by a particular site doesn't mean that your listing will appear on any particular search. Even if you're selling something obscure, like, say, Polish Sausage, a search on AltaVista finds over 3500 webpages, only 10 of which get on the coveted "first page." So registration by itself isn't enough; you have to have web-pages that "rank highly" with the search engines. I've already mentioned my page on this topic, and there are also tons of great sites out there that can help you learn how to improve your rankings; I particularly recommend Search Engine Watch as a good place to learn about how search engines work.
Finally, while registering your site (and getting good rankings on the search engines) is an important part of site promotion, it is important to understand that it is only one part of the process; there are other equally important things you should do (read The 500 Sites Fallacy for more thoughts on that subject).