Keeping Windows taskbar buttons always in a same order helps to minimize the effort needed to find the right button.
I have been using TaskArrange for ages and it is also working quit well. Nice thing about it is that you can even order the buttons inside groups. You have to open the program in order to arrange buttons so if you place the program shortcut in the Windows quick launch area it is near the taskbar buttons and rather handy to use. On the other hand, there is no need for running background process. Taskbar Shuffle process seems to have about 6 MB memory usage.
I think Taskbar button ordering should be an option in Windows, but these programs fill the gap. Well, nice feature would be an option to save the preferred order. Are there any?
There is also a japanese Taskbar++.