I have admittedly shallow dreams of one day having a personal assistant: Someone to make my plans and reservations then invite people to said plans and reservations. I wouldn't have to think about logistics, I'd just worry about getting to the event and having a great time!
HeyCosmo is the closest thing I've found to a PA — only it's online and nonhuman (so you don't have to pay anyone's salary).
HeyCosmo's Concierge does it all — they can look for a restaurant in your area with whatever specifics you need — number of people, location, time, special requests. Just enter these inquiries into HeyCosmo's website, they call with their automated service, and then HeyCosmo notifies you of which restaurant can accommodate you at what time. Of course, restaurant reservations are just the beginning; Concierge can basically make an inquiry to any business that you need it to.
Also, be sure to try HeyCosmo's Prankster, a text-to-speech service that will call your friends with your prank call!