Using 3D technology for computer screen privacy. It might be possible to use 3D-like polarising filters with a computer monitor to keep anyone else from seeing the same thing as you on the screen. As long as the monitor is capable of displaying two different images at different polarisations, and you have glasses that can filter for only one polarisation, you could display the private stuff polarised to match the glasses and display random noise pixels polarised the other way. Anyone looking over your shoulder would see only randomness, but you with your polarised filter would see the real image. That is if you can withstand the pounding headache.
Given the generally poor state of 3D, this might not work perfectly, but it should be a little more comfortable and less conspicuous than a giant hood, and more effective than an angle restricting filter. And you wouldn't have to use it for the whole screen all the time, just for sensitive things like password fields, email or chat windows - things you'd rather not have anyone read over your shoulder.
Mokalus of Borg
PS - This also assumes that nobody else has their own privacy glasses.
PPS - That's probably the biggest security hole.