How strong are skyscraper windows?

A MythBusters episode actually covered this.

The results are here:
http://mythbustersresults.com/pilot2

And the answer was yes, they’re not strong enough to resist you running through them, and at least one person has done so and fallen to his death. Though some posters on that page start to quibble a bit about it. It would depend on the window and what exactly happened.

Also the point of impact is important. A window resist impact more in the center and breaks easier if hit in the corner. The reason for this is the glass actually flexes when hit in the center and the framework makes the glass resist flexing in the corners. As a firefighter we are taught to strike glass in the corner for this reason. We also discharge a CO2 extinguisher at the impact piont before striking it because the cold makes the glass less flexable and causes it to break easier.