It's 9AM, and you're at home getting dressed to go to work. You've got iTunes open, and "Back in Black" is playing. You're totally into it, rocking out with your air-guitar, but you've got to go to work now. So you obviously want to keep listening to it on your way. So you pause iTunes, open iPod.app on your iPhone, find "Back in Black", and start playing it.
We've all been there, so you know why this sucks: you've interrupted the song! The groove! The beat! You just killed it.
Meet Seamless. When you're ready to transition music from iTunes to iPod, tap Seamless on your phone, and boom. The music fades out on the Mac, and fades in on the phone.
Beat: better than ever.