You know, they USED to wait a long time untill they released the DVD (or VHS) of a movie. Somethimes even asfter it was released to video rental stores. I remember waiting close to a year before I could buy Star Trek: First Contact.
Now a days, though, it seems the DVD is released 6 months after the movie. I saw Goblet of Fire in November, and in March I got the DVD. Same with V for Vendetta- the DVD come out next month,a dn I feel like I just saw it in the IMAX. Some times a movie comes out that your interested in seeing, ut hten you figure you'll spend over $20 at a theater, so why not wait untill it's out at Blockbuster and save a few bucks if you only have to wait a few more months?
Of course, Hollywood is starting to find ways to make money off of the quick turnaround. They release the barebones DVD, then release a 'Special Collectors Edition' with the bonus disk that has ALWAYS been included for free for $5-$10 more (Chronicals of Narnia, Batman Begins, Goblet of Fire). Then a few months later they release the uber-special directors cut for about $30 (Underworld, X-Men 1.5 comes to mind).
As for downloading, as a rule I try not to download any movie I don't plan on buying later on. I did that with Episode 3 and Serenity.