I am currently in the middle of a reorganisation of my writing inspiration boards on Pinterest, which has led me to think about how I use the site and the way I organise my notes and ideas more generally. There are a few different formats I use:
I use Pinterest for ideas on character appearance; locations; book cover ideas and (this is what it's the most useful for) outfits. Usually, if I go into detail on a particular dress or outfit, I've pinned a picture of something similar to it. I have boards on Arcan (including some great photos of silver hair), Helian and Brizan style on Pinterest. There are also a few images of Sephan style in my board for Water. Sometimes, however, I use Pinterest more to capture a particular mood or setting and there are lots of pictures of roaring flames on my board for Fire and the sea on my board for Water. Of course, Air has it's own board too, with some inspirational pictures of the sky and snow as well as this and this, which I won't explain just yet, but will become clear when you read Air later this year...
I use One Note and (for my new novel, Amber & Ice) Scrivener for more general plot notes: chapters to rewrite, ideas to work in, chunks of text that I've taken out for the time being, but might want to re-read at a later point. Both programs make notes easy to organise and find at a moment's notice. I also use these to keep track of name ideas, which is something I love researching and listing. For Elements of Power, I have a table full of different name ideas for different Realms. Most of them have been taken from baby name forums for unusual names. For Amber & Ice, I have a long list of classical Greek names which I check whenever I want to introduce a new character.
Not all of my note keeping involves technology and I have countless different notebooks filled with ideas formed when I am away from my computer. This is also where I have drawn my maps of the Elements of Power world, which have been invaluable when writing the series (and for planning a few novellas too).