Specifically, this one:
Although I had trouble adding a handful of other feeds earlier in the week. It seems the web app hangs for a long time while attempting to parse the feed, and I have to close the tab or refresh the page to get back to a usable state (FF 3.0.4 on OS X 10.5.5).
My suggestion: don't attempt to parse the feed immediately, just add it to the database (maybe a temp table) and parse the feed later so the user can continue adding URLs.
Importing/exporting OPML files would be a big plus as well.