To get updates on startups from the YC feed (and other like-minded sites), you can subscribe to this feed: http://www.seeksift.com/xml/6u106Rn2Hm/rss.xml and if you want to change the list of sites it uses to aggregate & filter content, you can do that via this link: http://seeksift.com/asp?act=edit-sources&id=6u106Rn2Hm
[/shameless plug]
Disclosure: my company, a micro software firm in NYC, developed SeekSift.