Doodle is not the only free online event scheduling tool but from my brief research earlier it looks like they all do much the same thing - others are mentioned in the comments on this Tech Crunch article. There is an excellent decription and review of Doodle on the Wired Impact blog so I won't go into details about how it works.
Like everything, using Doodle for the first time was slightly confusing, but conversely that was mostly down to the simplicity of it - I was looking for extra fields that needed to be filled in but that was me overcomplicating things. Once you know what you're looking at it is very straightforward and we had clear, concise instructions on how to use it. I can see how it would be useful for people trying to arrange a meeting with a lot of people ('participants', in nice non-jargony Doodle speak)...but only if most (if not all) of the participants engage with it, otherwise it would be immensely frustrating that people weren't using your lovely, efficient way of finding an appropriate meeting time.
I was also invited to take part in a Doodle poll by a colleague, and it is just as easy to respond as the invitee as it is to be the inviter.
You can even set Doodle to sync with your Outlook calendar, but you do need to register for a (free) account to do that so I did not try it. I did add it to my NetVibes page though, which is Thing 8.
Onto the next Thing shortly but first: