I use a PC...I use ACDSee to organize my scrapbooking elements. You create tags that make sense to you and then tag all of you elements.
The tagging of all of my stored elements took a long time, not gonna lie. But now it is so easy to find what I need, and I can drag it into PSE7 and we are good to go. Much easier to use than the PSE organizer. If you are just starting to collect digi elements, I would recommend plugging them in ACDsee right from the get go.
Ali Edwards is a hybrid scrapper who uses a mac, here is a
blog post talking about organizing her digital elements on her mac. She has a lot of great information specific to mac's on her site.
Good luck! Remember, you need to find what works for YOU!