Ah, ok. I wouldn't trust it myself, if only for interference from the other components inside the laptop. Plus adapters and converters isn't exactly a great signal chain. Then again, I'm concentrating more on studio work than live work. I too will be using the computer to make all my music, I just feel that an external audio interface is a vastly superior soundcard to the one that will come in any laptop. Let me know how you get on though, i'll be interested to know what it's like.
I'm hoping it'll be ok, no ground loop problems etc. Plus, the less kit I can take out live, the better.
Also, I assumed the latency would be better on the internal soundcard - no third party drivers, all fully integrated with Logic etc., Apple have full control over it.
Also, with Apple deciding to put an optical input/output on there (ie taking audio seriously on the machine), I assumed they'd at least have done a reasonable job on it.