I have an iPad 2 which can be connected to a projector. But my computer is connected to the projector all the time because I use the SMARTboard for every lesson. I wanted to be able to connect the iPad to the projector easily without having to unplug things all the time. I thought, "It would be really great if I could just flip a switch between the two." Well, guess what? Such a beast exists. It's called a VGA Switch Selector Box. There are quite a few to choose from and I went with cheap. I paid less than $9 for it. That may not have been the best choice, but I didn't want to spend a bunch of money to find out it wasn't going to do what I thought it would. This is the one I got. I also got a headphone splitter so that I can have the iPad and my computer hooked to my sound system at the same time.
The first time I plugged everything in and switched between the two, I was so excited. It worked great. I used it for my classes that very day. Then I came back the next day and was slightly disappointed. When I hooked it up the first time, my computer was already booted up and ready to go for the day. When I booted up my computer the next day with the VGA selector box already plugged into everything, it seriously messed up the resolution on my computer. I unplugged everything, plugged my computer back into the projector directly and rebooted. The resolution was fine again. I re-plugged everything into the VGA selector and it worked great for the rest of the day. So this means that I have to have everything unplugged before booting the computer for the day and then plug everything in. That's a big pain. It sort of defeats the purpose of why I bought the thing. However, it does make things quick during classes when I have it set up in advance.
I'm unsure if my problems could have been avoided by investing in one of the more expensive units. I'm still playing with it to see if I can make it work with fewer set-up steps. I use a Mac and you can set up a display control in your toolbar to quickly switch between resolutions. That's the next thing I'll try when I have time to play with all the different resolutions to find out what I need.