I think there is definitely a benefit from using it IF you're using it for the first time on an 80k motor, etc. If you're SeaFoaming or using gumout every oil change it's probably just going right out of your wallet.
I just had an epiphany (or however the hell you spell it)... if Seafoam does in fact not work... that means we're all ricers doing it just for the smoke show... *gasp*