I like to shoot the occasional panorama but usually the mood strikes me when the tripod is at home so I shoot handheld. With 2 or 3 pic panoramas that tend to go well but when I use more shots I always end up with a slight curve to my horizons. Any tips on how to correct this or to prevent this? (Apart from forking out several hunderd euros for a pano head)
There is an orientation tool in ICE to fix this. Look for the little 3D cube icon in the tool bar. Click on that, then you can interactively re-orient your pano. As you move your mouse around in this view you will see the cursor change between up-down, left-right, and an arc. These indicate which direction your adjustments will go if you click and drag. When you are happy with the new orientation click apply.
This same tool can be used to re-center 360 panos as desctibed here: http://community.research.microsoft.com/forums/p/2200/3295.aspx#3295