I currently log the total number of hours I work each day in an OpenOffice Spreadsheet. I input the start time, lunch/break time, and end time, and it calculates the total hours worked. I'm not savvy enough to create this type of spreadsheet myself, so I looked through a large number of templates online before finding one that works as I've described above. I'm still not crazy about the way that this spreadsheet is laid out.
If you can link to a spreadsheet available for download similar to the one described above, please do so in the comments.
If you use time-logging for various distinct projects throughout the day, please describe this process and link to the software you use (if possible).
More of a meta-discussion: how time-logging this enhanced your performance or time management?, for what types of projects/activities is it best to time-log?, general comments about the idea