MobileMe Galleries and multiple libraries
If you subscribe to Apple's MobileMe service (formerly .Mac) and have published one or more web galleries to your MobileMe website, there are a few details you should know about how MobileMe interacts with multiple iPhoto libraries and using iPhoto Library Manager. Note that MobileMe galleries are only supported by iPhoto 7 and later, so this does not apply to users of older versions of iPhoto.
iPhoto Library Manager allows you to copy photos, events, and albums between libraries, but you cannot use it to directly copy a MobileMe gallery that was set up in one library over to another library. If you would like to be able to access your MobileMe galleries from a library that doesn't have them already, you will need to re-download your galleries from MobileMe into that library. To do this, open up iPhoto's pereferences and go to the "MobileMe" section. If you have any galleries published from any iPhoto library, the list of galleries should appear there after iPhoto has a chance to check the MobileMe server. If you wish to download your MobileMe galleries to the current library, click the "Check Now" button, and iPhoto will begin downloading the galleries, which will appear in the "MobileMe Gallery" section near the bottom of the album list in the main iPhoto window.
When you download your galleries this way, the downloaded photos will appear in the gallery, but not when you look at the main "Photos" item that displays all the photos in your library, nor as an event when looking at the "Events" item. If you want your photos to appear there as well, select the photos in the gallery and drag them over to the "Photos" or "Events" item. You can then also include those photos in any other albums in your library.
MobileMe does not have any concept of multiple iPhoto libraries, so if you publish some galleries from one library, and other galleries from another library, they will simply all be lumped together into one list on MobileMe. There is also no way to pick and choose which galleries you would like to download, so you'll either end up with all your galleries, or none at all.
Important: if you delete a MobileMe gallery from within iPhoto, that will also delete that gallery and its photos from the MobileMe server. You will no longer be able to access those photos on the web, and if that gallery exists in another library, the next time you update that library's galleries, it will be automatically deleted from that library as well.