There are a few things Hulu+ has going for it, one is that the shows are in 720p, while regular Hulu is in 480p. But I've been watching a lot of Hulu through Hulu Desktop lately and the video has been really good. Maybe because I've upgraded my HTPC? And then there are a few shows that aren't available on regular Hulu at all. For example, the cancelled Fox show, The Finder, is only available through Hulu+. And the last time I looked, it wasn't even available on dvd yet.
But if you already have pay-tv and use a dvr, then Hulu+ is a big waste of money. I've been watching regular Hulu through Plex on my Rokus to catch up on stuff. Plex also has a CBS app (since current CBS shows aren't available on Hulu). Great to watch The Mentalist those times when NFL games crap on my Sunday dvr'ing.