I've just been playing around with time-lapse, piecing them together in Final Cut Pro. The piecing together isn't hard (although it does take she processing power), it's just working out the frame rate/duration when you come to to piecing it all together.
I shot some in work and set the interval time to two seconds and then pieced them together at intervals of 0.02secs in FCP, which gave the impression of life being speeded up but without it becoming a blur.
I've also done one of a road (check my flickr) that I shot at one second intervals of moving traffic. On reflection, that kind of duration is too short for what i wanted, although it's quite smooth. But 545 frames for 22-point-something seconds meant some serious shooting to get several minute's worth.
http://www.flickr.com/photos/patmacinnes/6851776853/
I shot in manual mode because I wanted any change in light (i.e. sun breaking through cloud) to really impact, although it didn't happen as we'll as I wished at the time. I've read that Av is a good mode - set the aperture and forget, providing the shutter speed isn't longer than the interval between shots.
BTW, once I'd done the image adjustments (LR3 makes this a breeze) I exported the frames as 720 pixel along the short edge - mono shots came out about 400k, colour shots about double that. It's worth bearing in mind the size of files you import into software, as this will dictate how easily your software renders everything.
There's some real maths to be done regardless to work out how frame rates dictate your shooting interval and the length of the film - good luck
