Would a Firewire HD be good for a laptop???

[MWink]

I'm getting a laptop and I would like a big fast HD to use with it. I know laptop HD's only run at 4200RPM which is really slow. I was wondering if I could get a Firewire enclosure and put my Seagate Barracuda IV 80GB HD in it and hook that to the laptop using the Firewire port. Would it work? How would the performance compare to internal 4200RPM drive? Are there any problems I'm not thinking of?