If you see lots of films, you know that many of them could be better. One easy example would be to lose the opening scenes of the otherwise very good Black Book and to tell the story in a linear manner rather than as a very extended flashback. No major spoilers in the first few minutes = better film. Similarly, the original Invasion of the Body Snatchers is better ending as planned, with the hero shouting on the freeway.
The combination of high quality source material on disc, Moore's law making memory and processing power ever cheaper, and a variety of affordable video editing software means that you can be a film editor and make a "fanedit". Some people take this very seriously, and spend months redoing soundtracks and visual effects.
Given how many Star Wars obsessives there are it shouldn't surprise anyone that there are dozens of fanedits of the films. Given how bad George Lucas is at things other than story-telling, it also shouldn't surprise anyone that nearly all of them are much better than the originals! So for example we can see how Episode 1 should have been (step one, cut nearly all of Jar-Jar's scenes). And there are Star Wars edits where Greedo doesn't even get a shot off, never mind having Han shoot first, plus a neat 'make the whole series into a 1930s silent serial' edit where that scene is lost entirely.
'Give these people a job as editor'
The Dark Knight remixed by Jorge – as with the original, not all of this works for me, but the basic idea – to concentrate on Harvey Dent as the character who actually changes during the film, and to have two narratives, one in black & white in chronological order, and the other in colour in reverse order – is genius.
Most of these.
Never Say McClory Again – Never Say Never Again with a soundtrack from the 'official' Bond franchise films and various other Eon-fications.
Braveheart – The Elerslie Edition – lose most of the unhistorical crap, like having a young woman princess fall for Wallace when she was in fact a toddler.
'Take this person's computer away from them'
I'm not going to name names here, but it's rarely a good idea to just stuff all the deleted scenes you found on the DVD back in the film. They were usually cut for a reason and it is noticeable how many of the good edits are shorter than the originals. Other people have shown that subplots can be a good idea.
As well as being on torrent sites, the editors also use download services like Rapidshare. In part so that you pay to remove various limits, they're often a pain to use for free. Fortunately, there is an excellent workaround in the form of JDownloader. This is a Java program which does things like wait for the time between requesting a file and being allowed to download it, ask your ISP to allocate a new IP address to get around download limits etc.