If a memo-pad works fine for you, great-- you probably don't need to put the effort in to construct something more elaborate.

But for me, the linear, static nature of a memo-pad renders it not particularly useful. You can't sort or rearrange anything without copying EVERYTHING in the memo-book over again in the order you want it. Mix this with crossed out items, changes you'd like to make but don't want to re-do the whole book for, and it gets stale VERY quickly.

I use a simple memo-book for capturing thoughts, random to-dos, etc. Then, if it's not something I can just do right away and get done, I transfer it to my action/project lists, my "lists", or my someday maybes. If you're familiar with the GTD system: I find it very helpful to have a section in my hPDA for "@Actions", with a seperate crad for each contxt, "Work", with actions project lists, and-or project cards for work, "Projects-home" with porject lists and/or project cards for home. If one card starts to get stale, out-of-date, gains lots of over-striking, or I'd just like to re-word it or make it neater-- easy to do, without disrupting the rest of the system. (I have seven other sections to my hPDA, most much thinner than the first three; I won't give the whole description here.)

I always have more ideas for things I'd like to do than I possibly have time do do them all-- so the GTD system has REALLY helped me, to prevent my mind from becoming tangled with maybe's, someday's, canI's, and where-was-I-with-that's.

PS-- I DO ride a train-- I spend three to four hours a day on the train. I love the little plastic 2cm wide case I have for my hPDA, since I do most of my reviews on the train-- the cards aren't clipped together, and I can turn the section or sections I'm working on "on end" to make them easy to flip-through, yet they'll stay in place even if I'm juggling other things.