If I were you, I would make sure to set the mouse at the screens center at application startup.   Mouse.SetPosition(centerx, centery);

I probably won't be able to answer again for awhile, (going back to work) but how far off is it on startup.  Before moving the mouse? Does the distance grow while the mouse moves? If you move the mouse outside your game during play, then do something with another application and move the mouse around, then go back to your ...

How far off is it? Is it consistantly the same distance off?

It's not a bug in XNA but something is wrong in your code. Why don't you turn on the windows cursor, to compare against. this   .IsMouseVisible = true;          

Your code snippit will work just fine. The error lies elsewhere.  How did you generate the texture2d?

I really respect your opinion JWatte, so I have a tendoncy to listen and take your advice. But it seems, that it is possible to query the heightmap for a light based value.  Such a function would return a value that could be used in the any shader, for vertices that have that height or greater. Would it be perfect?  Probably not, but ...

Thanks for the update and link to your CSM in progress. I was looking at CSM's as one alternative yesterday. But before I try CSM's and look over your new code, I'm trying an older techinque, that has nothing to do with deferred shading at all.  In this method, I calculate for every heightmap value, the current shading for ...

I'm looking into ways to properly shadow my terrain. I'm begining to think I've run into a buzz saw with this topic. It seems like a lot of the current shading techniques (Matt's included) cannot be used for landscape.  I may be wrong, about his because I haven't tried to adapt it to my large terrain.  (1024x1024 - with ...

FYI. I went to build you sample and it failed because I don't have the "Consolas" font. If you ever update your example, you might want to switch that font for a built in font. Seems like a good article.

I just went to your site. No wonder you wondered about how I was going to do my shadows. I'll check out your article.