external hard drive as a portable transfer method

I have a Powerbook G4, an iBook, and an iMac. For years I've lugged a
laptop back and forth to work with me every day. I've outgrown the
disk storage capacities on these machines. I'm fantasizing about
getting an external hard drive and carrying just that around instead
of the whole laptop, plugging it into whichever machine I'm working on
and having access to everything I've done at home or work -- plus
plenty of space to play with photos, movies, etc. In addition to
being a bit lighter, it would save me plugging in all my "stuff" after
each trip (power, printer, ethernet, camera cradle, etc).

1) Are the standard external hard drives rugged enough to survive
daily trips in a backpack, without fussing with extra "packing"?
(That's how I've been treating the laptop for years with no trouble).

2) If I work directly from the external hard drive, will it be
noticably slower than working from a typical internal drive? The
specs seem to imply that there will be no real difference - a 7200 rpm
disk with decent the same access time. And the USB2 and Firewire
interfaces both seem speedy enough not to bog down. But for data
intensive number-crunching applications, will I feel sluggish if I'm
using the external directly?

I was looking at the USB+Firewire Kanguru Solutions 80GB
KanguruQuickSilver USB2.0 Hard Drive, or maybe a Western Digital.
Open to other brands, but I do want both USB and Firewire since one of
the machines has only USB1, and it would be nice to have compatibility
with PCs that lack Firewire.