I’ve been a big fan of Apple’s Stickies app since way back in System 7.5. It’s great to be able to have a little floating place to type notes and keep track of things right on the Mac, without having to resort to anything as mundane as an actual, paper-based sticky note.
The one thing Stickies doesn’t do well is synchronize across devices. With OS X Mountain Lion, however, you can make this happen using Notes and iCloud.