Content Island is a way to pull out informations from UUBt and use them on a homepage. You can pull postings, topics (posting headlines), recent visitors and latest registered and approved users.
Ubbt will allow you to use several formats to do this: HTML as a Javascript file, HTML as a SSI or PHP include or RSS Newsfeed.
For siteintegration you can use includes but you have to notice something: several provider block the php include for safety of the server. To use SSI (Server side include) you need to have a .shtml webpage. The best way seems to be the java include but this can cause trouble with some browsers on the user frontend if they block java.
The use of RSS feeds inside threads is real easy. Opera and Firefox can use RSS by itself. To provide content as a feed you can simple put in a line in your UBB headerinclude like this example:
<link rel="alternate" type="application/rss+xml" title="last 10 News" href="/ubbthreads/ContentIslands/2_rss20.xml" />
2_rss20.xml is CI #2 and this is setup in the control panel for display the latest 10 postings of my news board. It's easy, try it.
Hope this helps a little bit.