I think like most people my response has to be that it depends on the DVD. I rarely buy with the extras in mind - and got the one-disk version of Superman Returns because it was half the price of the two-disk set - but sometimes find them interesting if they don't add hugely to the price. Director commentaries are often very interesting, ditto cut scenes and bloopers; I'm generally less interested in the other types of extras. But it's very variable - for example, the commentary on My Super Ex-Girlfriend is pretty boring, the commentary on Mystery Men is immense fun.
