Toshiba Satellite P20 here, 2.4 GHz, running Nuendo 2 and recording to the internal HD through a MOTU Firewire interface. Once the computer was configured nicely (disabled all network stuff, as this seemed to really slow down performance) I didn't have any problems.
Recorded up to 30 tracks simultaneously @44.1/24.
For smaller budgets and remote "studio" sessions, I have started to just bring laptop and interface (has 8 mic pres included) as I trust the stuff enough and there *is* a second chance if the system drops half a second of audio. For one-shot live recordings I still use a Fostex D2424 as backup device, and never had any issues except for occasional clicking when I forget to set up the proper clock signal chain (but that's my fault, not the computer's).
So, yes, if you have a reliable backup recorder, I think you can safely use a computer as main recording device.
Microphones always make me sound louder and better! -- Guitar Girl