Instead of saving older photos to an existing iPhoto library, create a new library. It's easier for both you and iPhoto to manage two smaller libraries instead of one huge one.
I'm not much of a gadget person, but I really love this new trick - thewireless photo memory card. All I need to do to transfer photos from my camera to my computer is... well, nothing! See why I love this so much and how it saves me oodles of time.