Imagine you had a digital camera with build in GPS and a compass for direction...
Imagine that GPS information is saved with every picture in EXIF-data...
Imagine there is a server you could upload your images of places you had been...
Imagine a software like Google earth would allow you to get to a point on earth, watch those images people have taken there and lets you even browser through time. How did that place look 5 years ago? How does it look in winter, in summer? Just walk through images and explore that place seen through the eye of different people...
Feasibility? Easy.
Benefit? Fun.

Did you notice...
...quite a lot of software uses themes/templates to customize the look of a document without changing the content. The most popular and well known use is definitely HMTL with CSS resulting in a division of content and the look (style) of a page. You can design different styles for web-viewing and printing like you might see on this page (print it!). Or simply apply a new theme to modernize your site.

This great ideas slowly reaches every part application development. What is the content - what is the look? In iDVD the way the chapters are arranged (plus the movies) is the content and you can change the look and feel of the DVD by applying different themes.
The same is true for many other applications like internet-content generators (RapidWeaver or iWeb for html or iSale for ebay), presentations (Keynote) or even text-editing (Pages).

My question: What is next? Any new ideas or have we reached the end of all possibilities - quite likely not!
What it boils down to is that an application must have some way to present its content - so that this presentation can altered. If you alter the appearance of the app itself we would call that skins - a little bit outdate probably because uses get confused if every application looks different. This approach has proven the be wrong.
So which field can be conquered? Plain editing apps - frankly, I don't see a chance here... An image or sound editor without export to anything other than native formats? If you can do a slideshow we're back again.

But take Google Earth (my favorite game right now). It has a lot of potential!
The content should be the pin-points of locations (as geographical data) whereas the look could be satellite images (as it is now) or 3D contours of the landscape, populations density or anything alike - plus you can overlay them in some way (thus applying multiple styles).
Mmmh, style inheritance just like CSS...

Just my 2c.