(And yes, the main caveat is that you do pretty much need a single-desk setup for this. Then again, I would argue that having a single workspace might be better for performance anyhow.)
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A lot of people just keep thick journals, but I like A6 cards that I compile into slim exercise books. I just capture anything that comes to mind on a card[0] and let them sit on a pile. Then, after some time, enough stuff has accumulated and I review the cards and compile them.[1]
It has the sweet spot of not having to commit to something big (meaning it circumvents the urge to make it perfect, usually preventing you from writing it down in the first place), is reasonably flexible if you use masking tape to glue in the cards (there are some books that I could take apart completely and reuse) and can be stashed and sorted easily.[2]
An even lower bar (in terms of commitment) than the cards are whiteboards, but I lack the nerve of putting one up. I also think that I'd hardly maintain them properly, so they'd end up crammed with stuff that I never really finish. The sweet spot that I've found for that is laminating balsa wood. You can get a 10 pack of balsa wood sheets (about .5cm thick) cheaply and just wrap them with clear adhesive film so you can write on them with a non-permanent marker. Bit of water and a tissue and they're good as new.[3][4]
[0] https://plus.google.com/photos/111011776153281260419/albums/...
[1] https://plus.google.com/photos/111011776153281260419/albums/...
[2] https://plus.google.com/photos/111011776153281260419/albums/...
[3] https://plus.google.com/photos/111011776153281260419/albums/...
[4] https://plus.google.com/photos/111011776153281260419/albums/...
(In 3&4, you can see how I'm copying and updating an existing concept to a new whiteboard, which is pretty simple if you can hold your whiteboard in your hand...)
Maybe I should finally write that blog post I've been thinking about for years now...