We've been shooting a show with the HDX900 on half shutter. The shutter were accidentally turned off. We shot a couple of days worth of footage. How dramatic will the difference be in footage?

Depends on if you're shooting interlace or progressive. On the former, you won't notice, on the latter it depends on how much movement there is in shots. If it's just talking heads the chances are you won't notice it much, but with movement it will become more smeary.

Bryan is right - If you record in 25P without shutter (like 1/25 shutter) the movements will be very blured. Interlaced would be like a 1/50 shutter. In Pal country.
If you recorded in 1280 50P you would probably not notice.

We're shooting 24P. All of our movements are minimal and very slow.

It mightn't be that noticeable, you can check it just by looking at the rushes.

If you were watching on a monitor while shooting you would see it live for the most part. It is a troublesome switch on many of the Panasonic larger cameras that the default is not half.

never had a problem with the shutter switch on my HDX900.I,d say its almost impossible to switch it off my mistake.. ?

I thought that even if you turned the shutter switch off it defaulted to a shutter speed the same as the frame rate, so if you were shooting at 25fps the shutter would be 1/25th.

I doubt if you will see any difference from a 180deg shutter of 1/50th unless you are moving the camera a lot but that will probably mask any difference anyway.