Just came across Timestamp...

http://www.syntap.com/products_timestamp.htm

Sorry to bump this old topic but i want to inform that we @ hesiod software just have developed a new kind of time tracking tool.
With the program you can fill in your hours at the end of day or week by looking back in the time.
It saves screenshots during the day.
So that you at the end of the day/week can easily see when and on what programs you have worked by the color coding of the different windows.
Sound somewhat cryptic but when your working with the program you will find out that it's not that complicated and instead will save you a lot of time.
We have both a trial and a free version available.
You can look for info @ http://www.hesiodsoftware.com ;

I used to have to juggle a lot of different clients and projects in parallel in the web agency I owned, since i did sales, client partner, support, general development (no, it wasnt just me, we were 20, but the buck stopped with me so i dipped a toe in a lot).

I discovered that I get so into the moment that I do not stop to record the swap from task to task, the interruptions, phone calls, or the meetings

A tool that helped me was one that records the details of the title bar and open files of the apps I have open, how much focus time and %of CPU they had. It also pops up a little window if I am been inactive for 5 minutes asking "what did you do? break?meal?phone call? meeting? for which project?" in an easy to deal with dialogue (5 seconds max).

With that tool I can review at the end of the day and tell it which project each line was related to. I can make the assignment sticky (i.e. "file xy in word is project z" "site T in firefox is project R" "donationcoder.com is break" "email thread topic Q is .." etc) so after a week the daily review is quick.

It is the only way I ever found out to actually get an overview, all the systems that rely on doing it while it happens failed myserably. I am too much in all the things I juggle to have that meta "record task swap" moment

There's a utility here, is it called titlelog, that does a simple version of this, without all the mapping and reporting (which you could do in excel or...)