One of my aims when buying my Silhouette was to cut screen protectors. I'm sad to say it's not very good at this:
But I just got an idea - maybe I can use less force, but double or multiple cut? Haven't tried this yet.
Update 25 Feb 14
Ok I tried multiple cutting - up to 10 times - and it either distorts, or it doesn't cut through. Things left to try - double-sided cutting and 30° blade.
Update 15 Apr 14
I tried with a new blade. I could cut through the screen protector (after removing the TOP protective film) with about speed 8, force 15, blade 4, double cut, but it still distorts. I think using a hard cutting mat might reduce distortion, but there is a high risk of damaging the blade.
Update 23 May 14
Ok I've got the aluminium/aluminum Graphtec blade holder (CB09) and the 60° blades. Will probably make a whole post on them, but the good news is they CAN cut screen protectors without warping, barely:
The original Silhouette cannot cut through screen protectors without distorting them. It can still help, though. You should engrave the outline using as high a thickness as you can without distorting the protector (around 10), then finish off by hand using a penknife/X-acto knife. It's still faster and more accurate than ruler/freehand.
If you want to, you can buy a third-party blade holder, which supports 60° blades (search for the CB09 blade holder). These CAN cut through screen protectors without distorting, but you have to search for the correct thickness (around 10-15), and use double cut.
If you're thinking of getting a Silhouette just to cut screen protectors, don't.
If you already have a Silhouette and would like to cut screen protectors, it's worth getting a 60° blade.