Speaking for myself only, I've grown tired of the mountains of paper notes and scraps that have already started to accumulate just during the last two years. Also, I hate hate hate when several notebooks have to be flipped open in order to find that one entry....So I've gone almost exclusively digital with an eye toward speed and ease of use. And, even more than this, I want a one-stop-shop. That is, I want a single software program to serve ALL my needs, such as:
1. Serve as word processor / database for all world-building, dungeon, npc, monster states and notes.
2. Serve as an easy to use database for any house rules that I may be running.
3. Above all, I want all of the above cross-listed and in easy-to-use hypertext.
4. I want any particular monster stat, room or trap description, treasure or piece of local gossip to be accessible in no more than 2-3 clicks.
For my purposes, which also includes not wanting to have to learn HTML, I've found WikidPad to be the absolute best.
It is fast, easy to use, and provides everything I could need in a personal wiki. On the downside, you cannot import maps or images into your wiki entries. But this seems a minor complaint for old school gamers, and I can attest that personal wikis that do allow images (such as TiddlyWiki) are far far more complicated and less elegant.
Other than pen and paper, other personal information management programs that you find useful for both planning a campaign and dming at the table?