Why are you taking the piss? I have just made your idea way more convenient.
Instead of booting up off a liveCD (which IS slow) then installing bitcoin and waiting for the download, you can just fire up the netbook.
You can make a script that burns an encrypted wallet copy as well, do whatever you want, it's waiting there for next time you need it.
When you've finished the transaction you just stow the netbook in the safe again. If I had 25k BTC I would probably do this. I think it makes a whole lot of sense.
Don't sweat, I like taking the piss. Just yanking your chain...
My initial point was, that you don't need to access your wallet.dat in order to transfer funds to it, so as long as you're in piggybank-mode, a tiny SDcard in a safe seems the least error-prone way.
But you're right of course. If you can store a netbook safely somewhere and trust its hardware will remain intact it'll work. Just never, ever install any programs in userspace. And of course, see that you never use sudo for anything you're not 100% sure about. So thanks for your contribution (Ugh, that's me being nice, I hate myself already).