It's still in progress but I've got particles going.  I surprised myself in deciding to use Microsoft's particle sample on their XNA page.  Unlike some of their other XNA samples, it's actually good code, arranged in a Maya-like "Emitter and Particles" pattern that I would have adopted anyway. I modified it to use perlin noise.  For those unfamiliar, perlin noise gives you what looks like animated cloud or (in this case) flame textures, allowing you to get convincing motion without having to use as many particles.

I also added a fade-in to hide where they clip through the ground plane, but did not do the depth-buffer comparison trick that would hide clipping with other objects (I don't think i will add this since it's less noticeable).

I had to be quick with the "Print Scrn" key to get this shot.  The particles are used for a flame trail that only shows up when you hit the "boost" button, sending the ball bouncing all over the screen.  Here you can see the motion blur applied to the spinning ball as well.

Aaru is an XNA tech demo for PC / 360.  It demonstrates real-time depth map shadows, motion blur, depth of field, bloom lighting, particles, perlin noise (on the fire particles and clouds, shown) and simple 2D physics (applied to a 3D sphere).  There is also some basic lighting with normal maps.

Click the images for the full 720p versions. 

The philosophy was to create a 3D "tile-based" engine mimicking the feel of 8-bit and 16-bit era games with some extra 3D polish.

In the following image you can see the motion blur applied to the entire screen as the ball moves.  When the screen reaches the world boundary it stops and the motion blur is on the ball only.