I stick to using freeware like DVDx 2.2 plus the divx and lame MP3 codecs, which can bring a film down to any size you want - 750MB for a 1.5hr movie is a good compromise - although it's a bit fiddly and you'll tie up your computer for several hours as it rips and re-compresses. A good starting point for guides on how to do this is www.dvdrhelp.com

But, if you have the spare capacity and want to take lots of movies with you, it's a good technique.

I like to (illegally?) download TV programmes we can't yet see in the UK - 24, West Wing - using bittorrent and www.suprnova.tk - no need to worry about ripping your own DVDs and makes a difference if you've seen the in-flight movies before.