Do not use a polarizing filter or you'll have too much sky contrast. Better use a tripod. To determine it, put an object near the camera. As you rotate the camera around a point somewhere underneath the lens , there should not be any observed parallax of the near object with the far background. If you don't understand what I'm talking about, you can just ignore it, it's important only for pictures with both near and far objects.
Deformation Take a look at the two pics above.
But if you look closely, you will notice that the shadow of the building that spans across the gap forms an angle. My PanoWarp program will correct this problem by changing the shape of the pictures. I wrote this program to do by hand and better what PhotoVista or QuickTime VR do automatically, namely the warping of the pictures. Let me explain. When you take a picture, a point referenced by X,Y,Z in 3D space becomes a point on the film, referenced by x,y.