For what exactly? I think you'd have a hell of a time actually finding something that could utilise it.
yes, too bad there isn't a location manager on the mac (that receives the input from the iPhone), it would be great to have mapping apps, etc, on the mac.
the iPhone could be a great extension for a computer, too bad Apple isn't doing anything about that, merging chat and messaging (iChat), using it as a hard drive, or an extra input device (like a trackpad with an LCD), etc !
it's not hard to write an iPhone app that continuously sends the GPS coordinates to a mac, but there is no framework for apps to use that data.