Of all the meeting time brokers I've seen, Presdo is the most peculiar. Which means it's worth checking out. Unlike other apps I've covered (Timebridge, Jiffle, Tungle, Timedriver, etc.) Presdo's strength is not that it automates the selection of meeting times that work out for attendees (it doesn't), but rather that it helps script the dialogue that's usually a part of the back-and-forth in setting up a meeting.
What makes this service peculiar is that it does very little that you can't otherwise do through e-mail and Web surfing. However, it packages everything up so nicely you might not notice.
You kick off a meeting by typing into a plain English description of what you want to do, such as, "Get lunch on Monday with Joe," or, "Set up book club meeting with Jack, John, and Claire at Sparky's Diner." Then you get a screen showing what the system thinks you mean. It guesses at the times and dates, and you enter in missing information like e-mail addresses. It also helps you find and map locations for meetings.
Once your meeting is set up, the system e-mails the other attendees with your plans. They can propose new times and places. The whole back-and-forth is captured on your event's dedicated page. Once everyone buys in to the plans, attendees can pop the meeting into their calendar (Outlook, iCal, Yahoo, or Google).
I found setting up test meetings in Presdo quite easy and almost fun. But I'm also left scratching my head. Presdo, at the moment, doesn't give you any real insight into when it would be good for you or anyone else to meet, meaning the thorniest part of setting up a meeting--choosing a time--is still completely manual. Nor does the clever location finder link in to a service like OpenTable for restaurants or Fandango for movie tickets. And the natural-language starting gate for Presdo is cute, but it's not smart enough to obviate the need for you to carefully check its work on the event page that it creates once you type your plain text.
I like the idea of new, pure interface for scheduling meetings. And Presdo does do a nice job of keeping your e-mail free of hard-to-follow messages about meetings. But I want much better integration into other calendar-related services before I start to use it.