some factors which i believe are essential are:
* EzineArticles- Writing an article for EzineArticles will get you indexed not only because there are so many changes happening daily BUT also because EzineArticles will place your initial article on the front page. In other words, Google won't have to reach deep into the website to find your link.
* RSS directories- Additionally, RSS directories are a great way to get indexed quick because not only are there a lot of changes, but many people will pick up RSS feeds and place them on their site.
* Social Sites like Digg and Sphinn- Once again, it happens because these types of sites are constantly changing and your site is listed in more than one spot.