I have 2 Passports that I currently use on both my PCs and my Mac with no problems. 1 Mac desktop, 1 PC XP format and 1 PC laptop, Vista format)
The only issue I have run into is when I had my Mac laptop HD data saved(water spill on my Mac, shot motherboard). The data is saved as my iPhoto data(original and edited). My Mac senses the info as a separate iPhoto Gallery. When I open iPhoto, I either have that gallery or my new gallery. I had to save them separately and then inport the old photos into my new iPhoto gallery as new photos.