One of the more interesting, niche applications to come out of MacWorld Expo 2006 is Parliant's PhoneHerald. It allows your Mac to automatically call someone, deliver a message, and record or otherwise handle their response. For example, if you're the secretary for a large community service group, you might use it to gather RSVPs for an upcoming party. At the end of the day, you'll know exactly who has responded, who wasn't reached, and how many party hats you should buy.
PhoneHerald lets you piece together messages from pre-recorded snippets (voice, music, etc) and text files that are read over the phone using text-to-speech. (I know what you're thinking, based on the demo video, the quality sounds OK.) It does all of its work in the background, freeing you to use your Mac (but not your phone, of course) for other things.
Having a product like this for the Mac is good news, Parliant's Phone Valet is reliable and easy to use, and I'm guessing that PhoneHerald will be, too. This type of product seems to be quite popular for some businesses, particularly schools and pharmacies. (Which I know because I get at least one automated, personalized phone call a week from both of these sources. Unfortunately, they're calling for the previous owner of my phone number, but that's a whole 'nother story.)