I wanted to add a photo feed. Went looking for a way to just enter the address of the feed, but instead found a page where I could create a gadget from a feed.
Changed the presentation style to Slideshow, with a very nice result.
PS: It would be great if Google supported Realtime RSS. I updated my feed 45 minutes ago but the change still hasn't been reflected in iGoogle. (I know, they want me to support their proprietary way of doing notification, I want them to do it the open way. You'll know that Google has become a serious competitor when they take advantage of every open format and protocol in the interest of making their product work better.)