Don't Panic: DIY portable Wikipedia as Hitchhiker's Guide to the Galaxy Hack
Instructables has posted a great little how-to on creating your own Hitchhiker's Guide to the Galaxy...
This Instructable will set out how to construct what I believe to be a unique implementation of Wikipedia in an offline, portable device. It involves installing a stripped-down distribution of Linux on a Psion 5mx handheld, and installing a static HTML version of Wikipedia for use with one of two browsers. Most importantly, you do not have to be a Linux wizard to achieve this. I will assume a basic familiarity with computers, but you do not need experience with the intricacies of filing systems, compiling source code and the stuff that traditionally puts people off using Linux.
I'd prefer the Encyclopedia Galactica myself, but hey...
Wikipedia in your pocket, aka Hitchhiker's Guide to the Galaxy v1.0 [Instructables]

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The Guide is better selling, though.
I'd like to see for myself if it's more controversial than Oolon Colluphid's trilogy of philosophical blockbusters.
Ah, Psion. It's so good to see you.
I'm sorry, but those are not "large friendly letters."
It's obviously counterfeit.
I have a copy of the Guide in my pocket - a jailbroken iPhone.
You could always rig it to actually use h2g2.com, the BBC's Wikipedia wannabe that Adams himself created before his untimely passing. Not that it's better maintained or more complete or as easy to use as Wikipedia, but if you're going to go to the trouble of creating a device specifically in ode to one book, y'gotta accept the tradeoffs.
That depend on what the word "unique" means: Wikipedia on your Ipod.