There's a reason why testing is very important. Failing to test the system just before a show off can ruin your show. That's what happened with Windows 7 and touch screen devices like shown on two videos on this blog.
On the first video, the presenter is trying to show Windows 7's capabilities to work with touch screen by running an application that is similar to Google Earth (i don't know the name of the application), but it won't stretches just like in IPhone or IPod Touch.
On the second video, another presenter is trying to open a folder on the desktop, but when he clicked the icon, there is no response from the Windows and they have to finally use the the technician to fix the problem. Again, when running the same application as the above, the stretch won't work again
I'm sure it's so embarrassing