Setup a Lightroom Publish service for iPad photo galleries
I use the hard drive publish service to create galleries for my iPad. I setup iTunes to sync photos from a particular folder, and then setup Lightroom to publish to that folder. Each time I want to create a new gallery for my iPad, I just create a new published folder and drop the photos into that folder. Then I publish the photos. The publish feature allows me to update photos in collections easily, as well as setup specific sizes for export to my iPad.
I have also used published smart collections for my portfolio images. When I tag a photo with a particular gallery keyword, it gets added to the collection. I then just publish the photos in the service and I've got them on my ipad. It works really well!
Setup a hard drive publish service
Go to the Publish Services.
Press the + to and choose Go to publishing manager.
Choose Hard drive as the service type. Name the publish service iPad Photos
Choose to export your photos to a specific location. Make note of this location and instruct iTunes to use the same location for synchronizing photos. Do not choose to put in a subfolder.
Choose the format as JPEG, Color space as sRGB, and set your quality in the File Settings section.
Choose to resize your photos to fit the iPad in the image resizing section. I have chosen Width & Height of 1500x1500. This will give black bars if your photo doesn't match the aspect ratio of the iPad. You can also choose Dimensions and set a dimension. The output photo will be cropped to fill the screen. I have an iPad 2 and wanted to be able to zoom a bit, so I chose dimensions larger than the iPad.
Set the other options as needed -- sharpening, metadata, and watermarking.
Back at the Library module you should now find your new publish service. Create a gallery.
Right click the service and choose Create Published Folder.
Name the folder the name you want to appear in your iPad Photos app.
Drop files from the photo browser into this new collection.
Right click the collection and choose Publish Now.
Repeat these 4 steps anytime you want to create a new gallery on your iPad.
All you need to do now is to sync the photos on your ipad using iTunes.