I keep thinking of using a cloud based photo service just for this reason. Flickr or Google+ would easily hold my entire photo library for free, wouldn't take up any HDD space locally, and would be accessible and editable from both my computers, iPads, and phones.
I suppose you could have one computer be your master iPhoto library and then sync that entire library to Flickr, and then just browse your photos on Flickr from your other computer.