I'm a fan of Office OneNote.  And when combined with the technology of Live Mesh, it creates a killer user experience. 

I've been using OneNote at work for a while now.  Recently, I've been using it for more things at home as well.  I've created quite an extensive notebook to track the notes I'm making for building a new house for my fiance and I.  She, on the other hand, has created a notebook to plan our meals and shopping list and to store recipes. 

I love having information at my fingertips whenever possible, so I decided to add my OneNote notebooks to my Mesh.  Now when I'm at work, I can find out what we're having for dinner that night by just pulling up the appropriate notebook from my Live Mesh sync folder.  The real beauty in using OneNote this way is with its auto-save feature.  In OneNote, you never explicitly save the file you are working on -- it happens automatically.  It's just very cool that I can take some notes on my laptop and when I'm done just closing the cover without even having to save.  Then later I log on to my desktop at home and the notes are right there.  It provides a very seamless experience.