When I ported my game from XNA 1.0 Refresh to XNA 2.0 (Beta), the picking isn't working properly.
The pick ray jitters a lot and I guess it's the problem with Viewport.Unproject.
Whenever my view matrix changed a little bit, the direction of the pick ray changed back and forth.
I'm using the approach refered in the XNA documentation to compute the pick ray.

After I implemented my own version of pick ray generation, the jitter problem went away and everything went back to normal :)

This isn't happening in XNA 1.0, so I guess it's probably a potential bug in XNA 2.0.

Is there anyone experienced the same problem? Tell me why this is happening.

This is the sample program modified from XNA tutorial, hope it demonstrates something.

I'm using Visual Studio 2005 Team + XNA 2.0 Build 2.0.11022.3.

http://files-upload.com/files/677911/Unproject.zip

The link will be expired in 14 days :(

I've been having a look at that sample, and while I can't really see that you're doing anything wrong per se, the problem is certainly lessened substantially by pushing your near clip plane out to 10 or 100, which suggests to me there might be some floating point inaccuracy going on, perhaps when using/normalising vectors somewhere, but as yet I can't fix it for sure.

Pushing the near clip plane isn't quite a good solution to this, here's the method I worked out for generating pick ray:

void UpdatePickRay()
{
    MouseState mouseState = Mouse.GetState();

    Vector3 v;
    v.X = (((2.0f * mouseState.X) / screenWidth) - 1);
    v.Y = -(((2.0f * mouseState.Y) / screenHeight) - 1);
    v.Z = 0.0f;

    pickRay.Position.X = viewInverse.M41;
    pickRay.Position.Y = viewInverse.M42;
    pickRay.Position.Z = viewInverse.M43;
    pickRay.Direction = Vector3.Normalize(
        Vector3.Transform(v, viewProjectionInverse) - pickRay.Position);
}

Where viewInverse, projectionInverse and viewProjectionInverse are computed every frame using

projection = camera.Projection;
viewProjection = view * projection;
viewInverse = Matrix.Invert(view);
projectionInverse = Matrix.Invert(projection);
viewProjectionInverse = projectionInverse * ViewInverse;