Here is a very interesting article on various attempts to amplify a saw: http://hooksandladders.wordpress.com/2009/09/02/diy-music-more-musical-sawbservations-two-shows-two-saw-sounds-one-night/
I agree with her re. contact pickups – it totally ends up deadening the music. Playing into a mic on a stand is nerve wracking – You always have to be aware not to smack the mic as you bend the saw. A much more satisfying experience is to attach the mic to your cheat. See this example of a Musical Saw Microphone holder. Or a low budget option is to just use tape and tape the mic to your handle.
One more choice is to use a shotgun mic on the floor aimed towards the business part of your saw.
Finally, remember to dial the treble down all the way to eliminate any bow noise.