I've been thinking about something similar to this - particularly for me in relation to when bands bring out new albums or new TV series come out. I was thinking I'd probably tackle it a vertical at a time and find a source for the information (e.g. last.fm for albums, IMDB for movies/TV series) that can be put to use automatically. I reckon the simplest way to monetize this would be affiliate links in the alerts - the click through is obviously going to be pretty high (people have actively said they're interested in something) but I've never seen affiliates as a great source of revenue.