On ANY laptop I would recommend using an outboard "card" (why do we still call them cards when they're actually boxes at that point?) to input audio, since even with a company like Apple going for the best possible components (and having long since been cured of the "not made here" syndrome), the inside of a densely packed laptop is usually just electrically too noisy an environment for analogue to digital converters. (And I think space constraints limit any internal card to less functionality - two in, two out. ) The built-in output, however is topnotch. But as long as you're using the card for input, might as well use its output, often multichannel, too. (Plus you'll usually get separate headphone outs.)

Just to go off on a related tangent for a moment, I first ran into the problem of circuit noise with the old Digidesign Audiomedia II and III cards in old Mac towers (I heard the Soundblasters in PCs of the same era were even worse), and my solution was to get an rackmount A/D/A converter connected via coax to the AM III's digital I/O. Get the converters outside the computer was the advice I heard back then and ever since I've been leery of internal soundcards, with converters on them, that claim to be pro quality. (The MOTU 2408 mk II I got to replace the AM III a little later kept all the conversion in the rackmount unit and connected via Firewire to a basic card in one of the slots.)

However, I have recorded simple stereo audio, using just my MB Pro's own input, as part of recording several demo movies using Quicktime and iMovie, with the audio coming in from a Behringer mixer (analogue) and video from the built-in iSight. I didn't notice any noise but then they were Indian pieces with my Raagini drone box going the whole time, which may have masked any noise which otherwise night have been apparent in moments of silence.

example here: uk.youtube.com/watch

But I haven't really tested the MB Pro's noise floor/interference noise, since I like having the functions and multichannels of an outboard card. It may be quiet enough in these new models.

I have both an M-Audio FireWire 410 (for my older Powerbook), which I've had for a while, and a MOTU Ultralight which I use for either my Intel iMac (studio brain) or the Macbook Pro (travel and future gigs.)

When you're just working with audio loops already in the 'puter, in Live or Logic or Cubase or whatever, the built-in soundcard is fine.

True, optical ins/outs aren't quite wide spread yet (probably due to the fact its still expensive to use fiber optic). I just thought I'd point out a couple of pros in the situation to even out all the cons of the sound card.

If you can afford Apogee hardware, I would go this route... www.apogeedigital.com/products/duet.php

They're about $450 new

Apples built in DACs and ADCs sound pretty bad.