Some game demos are over 1gb these days, and with products like Steam, it's not unusual these days for ppl to dl whole games legitimately. Or it's possible to l a 1gb demo, play it, hate, so dl another one, hate that etc.
I downloaded openSUSE 11 the other day, to upgrade from openSUSE 10.3, that's about 4gb. A while ago I went through a phase of Linux distro hopping, so was downloading different isos on a regular basis, some CDs some DVDs.
Some ppl like to get involved with the home dev side of things, so could dl nightly builds of an OS, or various software packages.
As mentioned earlier there's loads of Star Wars fan films, Troops as another popular example,
http://www.theforce.net/ has loads to keep you entertained. I would guess shows like Star Trek etc have lots of fan films to.