Do you have a memory like sieve? Sticky notes are a great way to remember stuff, and with digiNotes you can put digital sticky notes on your Windows desktop.
digiNotes is a beta program, so it's officially still under development. However, it's completely stable, and seems to have all the features you need from a sticky note program and more. The notes themselves can be resized, opacity can be altered, as well as font and color. You can also add a clock-note, or a basic calculator note. All notes and positions are saved when you close digiNotes.
digiNotes places an icon in the system tray, so is fairly unobtrusive. It's also pretty intuitive - right click on a note to change some settings, global options can be changed by right clicking the system tray icon.
There are many ways of keeping notes, and if you're in front of a PC all day using digiNotes is certainly more environmentally friendly than using real sticky notes.