I work in television as a tech director DP and editor for Sony and CBS, used to work for MTV... have always used a laptop from powerbook G4 to the new quad core. Honestly the bottleneck for me seems to be inspiration and focus, changing up my location for work wether it's at a starbucks or on a balcony etc seems to be the best aspect for my overall productivity but that's just me. Also some clients need you to come to them if they want to shadow edit so mobility in my opinion outweighs the brute force that the towers have (that's their only advantage)
If you pair your macbook pro with a thunderbolt RAID you're in great shape. I'd stay away from retina for now though as the video card does most of the rendering and if it's busy trying to articulate a resolution of a screen 4 times higher than the standard macbook pro, you'll probably run into some issues with that.
On a side note I cluster the macbook pro with a quad core mac pro for larger jobs and it works very well. If the render job is a few hours plus I just process it on the tower to keep the macbook free for other work.
Most of my work is in 1080p using apples uncompressed codec if that helps
