Ya, my mbp is pretty much permanently setup on my desk downstairs now but wakes up frequently when my ipad tells it to play music over airtunes or I need to remote in to print, or do something else the ipad won't... I think both are still needed but the iPhone really doesn't complement my way of life any more.
Even looking at the iPad on its own... we only have a wifi version and the iPhone gives us NO WAY to give it any internet if we're away from home! Well, without jailbreaking of course... Being able to setup wifi tether on another device (Nexus One) is awesome companion for the iPad when it isn't by wifi.
I honestly think the $30/month data plans (+ extra base $$) for 3G iPads is a waste when everyone is already paying that for their smartphones... But, under AT&T's current tethering model, they WANT you to pay an extra $30/month. Unlocked Nexus on AT&T is the way to go I think. 🙂