A lot of the attention Publish Services has gotten revolves around the link between Lightroom and online services such as Flickr, Zenfolio, SmugMug, etc.. But the other side of this feature is the ability to create links between Lightroom and your drives. And it is this aspect we will exploit here. Start in the Library module in the left panels. Go to the Publish Services section. There you will see a service entry for your hard drive. Press the Set Up... button to create a new service for your drive.
In the Publish Service section enter a description of your service. Then choose an export location. In this example I've used my home folder. Be particularly careful choosing this as you cannot change it once the service is created. Work your way through the dialog. The values here are from Matt's preset.
Now the Service has the description you gave it and shows the directory you chose. While you can put images in this directory to publish I usually use this as a reminder of where the images are. I prefer (and recommend) that you take advantage of folders and folder sets to organize the images into the different albums you want on your iPad. So click the + sign next to Publish services and in the section for your service choose Create Published Folder Set...
Give each of your albums a name and make to select the set you created earlier. If you have images selected when you create the folder you can also check the Include selected photos box. Otherwise you can drag and drop images into your folders later.
Once you have your folders set up you can drag and drop images into the appropriate albums (i.e. folders). New images dropped into the folder will need to be published. click on the folder in the Publish Services section and press the Publish button.
Why should we go through all of this trouble? Won't the first method work just as well? The real payoff is once the service and folders are set up then Lightroom will keep all our changes in sync. You can easily remove images from an album. And you can see from the service what state any of the images are in (to be published, modified and ready to publish, delete and ready to be removed, etc.) It's just another (and easy) way to manage your albums.
If you look at your drive you can see the correlation between the folder set and folders and the drive.