Drew,
Thanks for the thread and link. Do you use the Hyperdrive instead of a laptop, or in conjunction/addition with a laptop?
I have seen many items like the Wolverine, Hyperdrive, Epson, etc, which would be great for travel. But, I am new to U/W photography and really think I need to look at some images closely to see if what I am doing needs corrrection.
I like the WD link, the 500GB is $30 off right now. That could keep me bust for a few months.
Further, on another thread I saw some info about NetBooks. Much smaller than my 15" MBP and at <$400, I'd feel better about traveling with it. Of, course, I'd still want a portable drive to as backup.
Thanks,
I use the Hyperdrive in conjunction with my computer and external drives. I will make a copy to the Hyperdrive, at least one external then my laptop before I start touching anything.
I also have a boot partition with utilities on one of the drives just in case and with the larger USB pen drives, also have been able to fit it on those. Of course since I started that, I have not needed that, but one trip I did, so started that procedure 
Of course there all of the drives are in the same place, but I am often in places with room safes and put one of the drives in there. Never had an incident though. It is not a bad idea to have a computer like you said, and size is a consideration. I am a Mac person myself, and my main laptops now are a 15" and 17" Intel machines. The 17" is great for longer trips especially if you are settling down in a place for a bit of time (such as hotel, condo) though the weight and size can be difficult especially when carrying all the other toys (I also carry a video rig). In other words when I have taken the 17" (like most of the other equipment) my poor wife listens to me curse until we get where we are going, then listens to me say how happy I hauled everything once I hit the water and plug things into the wall 
The 15" inch is a balance for me in terms of size performance, though I still kick around the idea of either an Airbook (though only 1 USB port gives me a bit of concern sometimes, but you can get refreshed Airs fairly inexpensively) and the new revision 13" MacBook Pros with FW added back in is also something I am considering. [used to carry a iBook G3, rugged and was fine, but did get long in the tooth eventudally]. I find myself working less on the photos/videos on a trip (other than to download and take a quick look) and more trying to enjoy the trip, figuring I can edit and the rest back home. So either of those models will have the horsepower I practically would need. But I have not made those jumps yet. If I get closer to a dive trip (unfortunately non on the near horizon) I may revisit the issue.
The netbooks are interesting (and hoping perhaps in the not too distant future there is a Mac one), and I been tempted, especially since I know people have gotten OS X on them, though I think it is a bit small for my needs (email, surfing, quick looks.) A buddy of mine has been traveling with one and thought it was a bit small for his use even for emails and he is shorter/smaller than I am.
As to the WDs, like any HD, smaller sizes are cheaper. The 500 Gig (with FW) is abut $179 at Best Buy 500 Gig USB $139, 320 USB $99. You probably can find better prices than that. I acutally have Seagates, OWCs and Lacies also. Have not had real issues other than an occassion port going bad a couple of times. The WDs are fairly thin, which I like. The Lacies Porsche Designs are thin, though they seem to get a bit warmer to me, though I never had a problem with them.