This is something we did last year and it was a great success. Friis Alexandersen, an American photographer, launched the initiative and it went International. A true display of how the Internet can help to get the ball rolling! I think we had somewhere between 40 and 50 people turn up. Some as couples, some as families, some just as friends, but we shot them individually, together; all ways. Then we rushed to photos to one of the two computers we had there, loaded them up, selected the best one, retouched it as necessary and then printed out an A4 photo that they could take with them.
A really useful site for you to look at is MCP Actions. Here you can find all sorts of stuff to help improve your photography and Photoshop skills, most notably, a very impressive array of actions. For those who don't know, actions are basically recordings of steps one can carry out in Photoshop to achieve a particular result. If you find that you regularly perform certain tasks in Photoshop, you can create a new action, start recording, perform the steps you normally take to carry out this particular task and then stop recording.