As a PhD student I generate a lot of pages with calculations, ideas and lecture notes.
Most of them are useful only for a short amount of time, but some may be important for much longer (when writing a paper, or when having new ideas to continue a once abandoned project). Typically I work on a few project simultaneously.
The question is, what is a good practice of taking and keeping notes? (With or without computer apps.)
Writing on single sheets (even if adding date and title) makes it easy to organize by topic, but also easy to loose. Keeping in one notepad makes it harder to collect useful things of one topic in one place.
I find that a mix of both worlds (physical and digital) works best for me. People have different ways of retaining and processing information.
Productivity apps are quickly becoming a popular and efficient choice in managing note, documents and other information. You may want to try applications like Evernote, Dropbox or Google Drive or a mixture of the three.
Also recognizing this growing problem of information overload and how to address it, there are many new and improved data capture applications that cater to the myriad of problems stemming from the need to organize information efficiently while making it accessible no matter the age of the info. You may want to try new apps around like Doo or Phoenary to enhance your note-organizing and information capture.