I'm curious as well, though with the selection of movies they currently have available as 'Watch Instantly', not sure if it'd be worthwhile right now.
Out of a relatively wide mix of genre and movie release dates (1978-2008), my queue of over 90 movies only has 9 movies that could be viewed with the 'Watch Instantly' option. For clarification, almost all of these titles are commonly known, not some of the terribly obscure titles. This amount would need to be quite a bit more to intice me... -TD