click to enlarge, or see it on Flickr
First of all, you don't need to have a picture of a massive landscape. It just can't be a close-up picture of a single subject; there need to be some "background" type elements present to provide perspective and feel to the photo, or the tilt-shift effect won't really work.
Second, you can use a radial gradient rather than a reflected or cylindrical gradient. It all just depends on what you want the photo to look like in the end. Different gradients work better for different photos.
This isn't a particularly spectacular tilt-shift, but I like how it looks, and it was a good exercise. Feel free to post more links to your own tilt-shift work in the comments!