I just wrote a blog post about an external trackpad for the Mac with multi-touch (found here). But wouldn’t it be cool if someone wrote an app that allows you to tether your phone to your laptop and use it as a multi-touch trackpad?
All you would have to do is open the app on your phone and you’d be able to control the mouse on your screen. You can control your lights from your phone and your iTunes from your phone, so why not your mouse? For all i know the app might already be out there. If it is, someone tell me, otherwise, someone write it 
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18 Jun 2009 at 16:37
There’s a paid app called Air Mouse. I use it a lot since my home desktop is directly connected to my TV for netflix, media center, etc.
http://www.mobileairmouse.com/
21 Jul 2009 at 15:07
Just try snatch. I use it, and i love it.
Mouse, multi touchpad, remote controller… All in one.
10 Jul 2010 at 05:02
Look out for iTouch server & TouchMouse (or iTouch) for iPhone, by Genious. It's free!