My non-novel solution - number every other page, and keep a few pages up in the front as an index. Topic on the left, and a list of page numbers on the right. Requires some effort to maintain, but it seems to work pretty well for me. Familiarity with the index pages counters the need for any sorting.

I have a fat notebook with lots of pages. I write an index in the back, with a colored "tab" on the edge of the page corresponding with that index item. Any time I make a note about that item - call it "blog post ideas" for example - I mark the edge of the page my note is on with the corresponding index item.

I don't think I'm doing a good job of explaining this, I'll see if I can find an example of this online and link it.

Edit: I did a quick google search and found an example that's similar to what I'm doing. This works well for me: http://lifehacker.com/mark-page-line-edges-to-organize-your-...

I've run into the same problem before. I found that Bullet Journals have a good system for this. And it is applicable to any notebook you have. (Similar suggestion was made earlier in the comments.) Link: http://bulletjournal.com/

I don't. I transfer long-lasting notes to a wiki or relevant documentation. I on purpose try to integrate notes into something existing, and/or archive them regularly