This post'll be more useful as more people chip in with their diverse methods, so here're mine.
At home I almost exclusively take notes on my PC, where I use MediaWiki, although in retrospect MediaWiki's probably unnecessarily heavyweight. (Everyday use is straightforward but it's cumbersome to install & maintain.) Very occasionally I make & save computer algebra system notebook files.
In transit I don't have an easy way to take notes, but I recently bought an e-book reader and installed a simple notepad application on it. I'll see how that goes.
On campus:
An idea might grow & transmogrify into different formats as I experiment with it. In extremis, an idea might start as 5 or 10 words in the margin of a printout, become a clumsy stream of improvised maths on some scrap paper, get upgraded to a more systematic derivation over a few lab book pages, generate a few emails, then grow an abstract and figures as I turn it into the outline of a potential paper.
Do you take any notes on paper? If so do you scan them or otherwise digilatize them?
I don't systematically scan or digitize paper notes. The nearest I come to that is manually expanding scrappy notes into better-written notes on my computer if I (expect to) try to rework them into a proper project.
Do you have specific strategies for deciding which information to write down?
Nah.
Do you tag your notes?
I use categories in my wiki entries, but that's about it. For other computerized notes normal search tools usually suffice, and I manually search my lab book based on entries' dates & titles.
how private are your notes? Would you allow friends to read in them? Your spouse?
Pretty much. The most embarrassing things in my work notes are little comments like "Oops that's wrong", which is no big deal. Almost all of my home notes are innocuous to the point of being boring, as they're things like extracts or references from books. There is the odd blunt/rude comment about other people in there, though more about authors/public figures than people I know.
Is there some reason you use MediaWiki rather than a personal wiki software (for example Zim)?
We all deal with a lot of information. What are your strategies of taking notes for new information?
Do you take any notes on paper? If so do you scan them or otherwise digilatize them?
Do you have specific strategies for deciding which information to write down?
How do you write notes to capture all important information?
Do you tag your notes?
If you use Evernote, or a similar system how private are your notes? Would you allow friends to read in them? Your spouse?