Pixel Shaders are awesome!  I've been playing with Pixel Shaders lately... went through the excellent Custom Shader tutorial in the XNA Developer Talk series, and then did some experimenting of my own trying to make a respectable shockwave effect.  My shockwave effect went through several iterations:

1) Stationary effect controlled by a texture (a radial gradient)

2) A programmatically-generated effect in the effect file

3) A programmatically-generated effect that is controlled in my code, with several key variables passed in to the effect file (XY location, distance to shockwave from origin, and width of shockwave)

4) An array of shockwaveParam objects passed into the effect file and applied to the image.

Very fun stuff to experiment with :) Here's a screenshot showing number four in action: