I'm not a manager implementing this time tracking service at work so all I really care is if it is intuitive to use and does not distract my work. Harvest does it well! All I need is to select the project/client and write down a little description on what I'm going to work on. There are times I forget to start/stop the timer, but it is very easy to go back and fix such mistakes. It integrates with the widget on my Mac OSX well as well.

I use Doodle to figure out a best time for weekly meeting my class project and for the student club I run. I also use it to take a poll to figure out a best day for my friends to join my party. Doodle so simple and intuitive that anycan can create a poll quickly and send it over with automated reminder for those who did not take a poll yet. I also love that I can visually see the result of the poll realtime, and it is easy to take an action based on the result.

I recommend this tool when you need to take a poll from many people with conflicting schedule. However, I cannot recommend this to make an appointment with just one person because it'd be faster to just call the person.