usually the under-500mb ones are camcorder recordings, where speed (getting it from the theatre to the net) is more important than quality.
the 650mb and above are usually rips of DVDs/VCDs etc, months or years after cinema release.
I just can't take the cams and go for the rips, but then I got DSL; for others I guess there'll always be a place for smaller files.
Also I go for the rips coz I usually only d/l movies that crashed my PC when I rent them on DVD. F#k Hollywood if they're gonna press sh1tty discs!
I just wish people would make sure to mention when it's a cam so I could avoid it.
(I got tricked once assuming a 630mb file was rip; instead I got perspective, sync trouble and Chinese/Malay subtitles & chitchat).
But it will all be better soon with the help of Sig2Dat, FastTrack's P2P Movies and FastTrack Central... until Sharman screw things up again at least.