At least a couple of people have shown an interest in being able to generate circle primitives. I needed to do exactly that earlier today, and because neccessity is the mother of invention...

KML Circle Generator

It's not a real solution, but it's a pretty useful hack. It'll generate a LineString path for you that looks just like a circle.

You'll need the coordinates of the center of your circle, and either a radius (in meters) or the coordinates of a point on the circumference.

I haven't tested extensively, but it seems to be fine for the most part. (Theoretically there's a chance it'll b0rk if you try to do anything near the poles, although I haven't made it do that yet.)

Comments, improvements, bug reports &c all welcome. The source is here.

[Note to math geeks: I'm using a slightly modified Haversine formula to calculate the distances. It's pretty accurate, but because it assumes a spherical earth, it grows slightly inaccurate over large distances.]