After reviewing all the Digital Asset Management and Photo Editing titles I could find that would run OS X, I opted for Adobe Photoshop Lightroom. It has most of the features I need, a few features lacking are still in Photoshop CS3, but for the price, I couldn't argue. I like how it runs on the MacBook as well as the MacPro and it's simple to use. Can't recommend it highly enough.
For anything that needs converting to more web-friendly formats (e.g. for icons), I'll continue to use Seashore and Pixen after processing the photo in Adobe Lightroom.