Working in the semiconductor industry as an engineer, I can say that the industrial touchscreen controllers / tablet PC's used in the industry for controlling VERY expensive equipment and processes are robust, but not immune from occasional lock-ups or crashes. Some run windows NT or XP, a few run OS/2, some are even DOS based but none have been immune from these issues.
Bearing in mind that these are bought primarily for the fact that they are robust pieces of kit and they have a (usually very) good MTBF we're charged accordingly. I know that all the Apple / mac users out there are going to tell me that "if it was a mac, it wouldn't crash". That may be, but in a very high reliability / very high utilisation environment, kit like the iPad is unproven. There's a world of difference between personal use, industrial use (my area) and aerospace / defence applications, and it's not a linear relationship.
Basically, I think kit like the iPad might be a bit of a laugh in the cockpit of a C152 / PA-28 but is so far removed from anything in commercial aviation as to be an irrelevance.
Just so I can't be accused of being an apple hater, I do own a 5th Gen. iPod and I do quite like it!
But I do understand people who say that apple are primarily a form / design company with a few techie bits thrown in for good measure!