Photoshop represents one extreme in the software world — it's an expensive, very specialized piece of software that has piles upon piles of tools and features. Apps for phones and tablets, on the other hand, tend to be relatively simple and inexpensive, focusing on doing one or two things with ease.
Photoshop Touch will attempt to bridge that divide. While it won't act as a replacement for the real deal for power users, it will bring familiar tools such as layers to tablets. It seems likely that if you need to do some image editing and you've only got an iPad, Photoshop Touch will be able to do many things for you. And at $10, it's a tiny fraction of full Photoshop's price. Will you want to uninstall Photoshop from your laptop? No, but this seems like a great addition to tablet app stores.
What's best is that people don't have to be worried about lack of compatibility — coming out for both iOS and Android tablets off the bat is a huge move, bringing this software to the masses. Adobe hasn't announced the date when this thing will be released, but they are accepting email addresses to be notified when it comes out (and so they'll have your address for all time).