I don't use these at all. Partly because I don't always have access to internet, and so for those times I would be completely cut off from my work, and partly because not all my planning is digital. I find a notebook (paper variety) which I carry around with me is perfect for those moments when an idea strikes because it is instantly accessible and because it can be used for doodles, quick sketches, layouts, flow charts, text, etc. etc.
Some things I keep in dropbox so that I can access them from different devices, but that's about it.