When we first introduced you to the Architecture / Interior & Exterior project we showed you Photographer Mike Kelley and his unique style of image compositing.
I've found the older version of his website which showcases his before and after images that really showcase to you what can be achieved with this sort of project.
Take a look at some of his before and after images:
More of these images can be viewed on his website: http://mikekelley.squarespace.com/beforeafter/
Remember you don't have to shoot your images in this style but if you fancy taking on a real challenge that will drastically improve you understanding of Photoshop as well, then why not give something like this a go?