In the Virtual Earth v6 API, one of the new features is improved Birdseye accuracy.  The Virtual Earth v6 API has some new methods to more accurately position pushpins when in Birdseye view. 

Satellite (Aerial/Hybrid) and Road imagery views are direct overhead views, so calculations to position a pushpin at an exact latitude and longitude are not as complex as in Birdseye.  The camera is directly overhead the point and the elevation of that point on the Earth does not need to be taken into account in 2D.  However, with Birdseye imagery taken from different angles, there are a lot more variables to consider when calculating where to position a point including the camera position and the elevation of the Earth in that scene.

In order to do this calculation efficiently in Birdseye, a service request is made from the client to the server to get more accurate positions.  For some applications, the client-side, less-accurate, faster calculation may be enough to position points.  Because of this, enhanced birdseye accuracy for pushpins is off by default in the Virtual Earth API. 

To turn on enhanced Birdseye Accuracy for pushpins in the Virtual Earth API, you can make the following call (assuming you have a VEMap instance called "map"):

map.SetShapesAccuracy(VEShapeAccuracy.Pushpin);

To turn off enhanced Birdseye Accuracy for pushpins, you can make the following call:

map.SetShapesAccuracy(VEShapeAccuracy.None);

Here is a link to sample Virtual Earth application showing 3 points on Lombard Street in San Francisco with a checkbox which turns Birdseye Accuracy on and off:

Virtual Earth Birdseye Accuracy Sample

Notice in Aerial view, the 3 yellow dots are positioned at precise points along Lombard Street:

If you click on "Bird's eye" on the navigation panel and click on different orientations ("N", "W", "E", "S") on the compass in the navigation panel, you will notice the 3 yellow dots are still positioned rather accurately in Birdseye.

Here's a screenshot of the Birdseye scene looking toward the West with enhanced accuracy enabled: