Since Hub Pages content generally helps people, I like the smart phone idea and use it often. I will either use the notepad or the voice recorder, depending on what I'm doing at that moment. Keeping note pads in strategic locations where you spend most of your time is good. A friend of mine carries index cards around with him to make notes on.
For me, the most valuable information I have to share on Hub Pages generally comes from work. As I come across something that vexes me, I try to make sure I write it down. When I take a mental note, that note generally becomes 'sour' and disappears from my life.
The 'cloud' is a good place if you are online when a great idea comes along. Set up a Google Doc for ideas. You can even access Google Docs from smart phones.