The Ubuntu Developer's Manual team was discussing the instructional app that we should use for the manual. During this discussion, it became apparent that there wasn't a way to download from a URL that was both easy and also asynch. Instead of choosing between simple and good, Stuart made a Quickly Widget that provides a way to fetch from a URL that is both simple *and* good.
So, two lines! Just say what url you want to download, and tell it the function to call when it's done.
fetcher = UrlFetchProgressBox("http://identi.ca/api/statusnet/groups/timeline/8.rss")