Never Miss a Beat with GTD, Tagging and Microsoft OneNote
This guide is derived from what I learned about GTD, a helpful set of links, and doing what works on the job. If you are part of the modern workforce, you most likely spend your day jumping between a myriad of tasks: replying to emails; preparing presentations; creating financial models in Excel; designing the layout for a new feature; and the occasional quasi-human contact by picking up the phone.
I used to keep a physical record of what I needed to do, but it ended up becoming laborious and more often then not, I ended up missing out on important items.
I now use Microsoft OneNote to keep track of my work life. I spend most of my time on multiple projects that are in different stages and have many moving pieces. I am always taking notes and action items come up.
I needed a way to create a to-do list on the fly, and OneNote did the trick. By using its tagging feature, you can tag work items right in your notes and have them aggregated automatically:

This system allows me to be efficient by categorizing the kinds of work that I need to do. Here is what a larger list looks like:

To give this kind of task management a shot, all you need is Microsoft OneNote 2007 and 15 minutes of free time. I will walk you through setting up tagging.
Setup your Tags
I assign tags to lines in OneNote that are action items. OneNote even allows you to assign multiple tags. Here are the list of tags that I use:
processing - For items that I have not categorized yet
email - Emails I either need to write or reply to
discuss - Items that come up that need to be discussed
desk - Things I need to do at my desk like create a presentation or spreadsheet
review - For emails, documents, or links that I need to read and review
tracking-issue - Issues that need to be kept on my radar
later - Action items that can be postponed
idea - Ideas and features that need to be tracked
today - Items that need to be finished by the end of the day
Your tags may be different depending on the type of work and person you are. A Designer might create a tag called @photoshop or a Financial Analyst might create @sap or @excel.
Here is the set of tags that come with OneNote and what you need to modify them to:

To modify a tag, click on the Tag drop down, then click Customize My Tags. You then click on the tag and click Modify.

As you modify each of the tags make sure you select a Symbol that can be “checked”.

For the *today tag, make sure you select a Highlight Color.
Start Tagging
You can tag selections by using the drop-down menu under Tags or by using the short cut keys. When you are ready to see your summarized/aggregated view of tags, click on the Tag drop-down and select Show All Tagged Notes

You can now use this view to check off items that you have completed. You can hide/unhide checked items by clicking on the Show only unchecked items box.

You can also update the list by clicking Refresh.

Summary
Setting things up is easy. Just remember, if it feels like an action item tag it as @processing and come back to it later to assign the correct tag. Once you get the hang of it you will start to notice that you can track all the small details. One thing I try to do is attack a section at a time. I first start with all the *today tags. Then I move on to @email, then @desk, and so on. It keeps you focused and you start getting things done.
There are a few other features worth their own posts, so look out for them soon.