If you do anything that involves holding little bits of data and then using them from wherever you happen to be you will probably find EverNote useful.
It is a "cloud" application that lets you lob pictures, notes, web links, bits of files and whatever onto a central storage location that you can then access from your PC, Mac, browser, Windows Mobile device or iPhone.
It has some nifty search facilities, even being able to pull handwriting out of images you have captured as notes and then use them as search keys.
It seems to work really well, and you can use it for free if you don't want to upload much content. Even the paid service is not bank breaking, at $5 a month.
Whether you are studying on a degree course, running a business or just going shopping I reckon that it is well worth a look.