This question seemed so good I thought I'd answer it in a whole new blog post :)

As always, it'd be great to see software developers impress me and find new uses for this technology that I haven't foreseen.  I can't tell developers how to write a great application; but I can pick a great application when I see one, and I'm looking to you to impress me.

Transactional NTFS can't guarantee that changes you make to a set files will always be successful, but it can guarantee that on failure the result will always be consistent.  Consider an application install: if you can't copy a particular file, and want to undo all of the files you've already installed, what happens if your undo fails? Maybe a user has your readme opened, and locked, in their editor; maybe they've already moved your start menu entries; maybe they've deleted or moved files you carefully put there.  With Transactional NTFS, all of your changes can be removed - this is guaranteed.

A better example would be a patch or service pack.  If it succeeds, great, if it doesn't, that's okay, but if it half-succeeds, that's terrible.  Transactional NTFS will protect your application from inconsistency.

Imagine updating a website: you make some changes, but fail to update a particular target.  This leaves your site inconsistent, with broken links.  Transactional NTFS will protect you from this possibility; and better still, will ensure all your updates become visible at the same time, reducing the risk of inconsistent results.

When saving a document, some software will attempt to delete the old file, then create a new file in its place.  What happens if something goes wrong? Both copies can be lost.  Transactional NTFS eliminates this possibility.

Suppose on a network, you want to copy a large amount of data from one machine to another: Transactional NTFS can ensure this succeeds or fails atomically, preventing inconsistent results between servers.

These are my thoughts, as an developer.  How you can best use Transactional NTFS depends on your application.  You may have different ideas; I'm interested to hear about them, and I'm sure other developers are too, so feel free to share.