glass cover good or bad ?

[Aquattro]

To offer my opinion, I wouldn't think of adding any type of cover to my tank. My canopy will keep jumpers under water (as long as it's closed) and their is no way I'm sacrificing even 2% of my expensive lighting to being filtered by the glass. Temp is easier to manage and if you're adding kalk, you'll want significant evaporation to allow the addition of enough make up water to get the kalk in your system.
In the years I've had my tank, nothing has ever fallen in. Overall, I can't think of a good reason to have glass over a tank.