Downloading HD trailers from Apple.com/trailers

Where exactly are those trailers saved to? I click on a trailer I want to download and it opens up in QT. (Clicking on a second trailer seems to replace the existing trailer and open the new one instead.)

These can't be small files... am I inadvertently saving a bunch of these trailers on my hard drive somewhere, or upon quitting Safari or QT, are the files being deleted?

I suppose this goes for any other media content like YouTube that is opened specifically within the browser window... technically, isn't the info being saved to the hard drive?

I'm trying to consolidate and maximize space on my hard drive as I seem to be filling it up overly quickly. Every bit helps I think. Thanks!