I read of mixed reports from the USA about the Ipad2 overheating. Some had it, others never.
However it must depend strongly on whether there is direct sunlight, and how much cooling there is. I know this because I fly with a tablet (an old LS800) which runs
far hotter in direct sun, and
far hotter in the absence of ventilation. The LCD backlight also makes a big difference.
I reckon if you lay an Ipad onto your knees (i.e. no cooling on the back) and have sun on the top, and have the backlight on max (which you have to in such conditions) it would get way too hot.
If OTOH you somehow mount it in a holder, so there is airflow all around, it would be very hard to get it too hot.
The problem with any device that dissipates a few watts or more, cooled by convection alone, is that it will be extremely sensitive to what is around it. Fairly obvious really, given that conduction/convection/radiation is all that stops its temperature reaching infinity
