Since going on sale in Japan last December, there have been 31 incidents in which the PS Vita overheated, rendering the machines inoperable. As of early June, 23 of those incidents were in Japan, while 8 of them were abroad. Thankfully, no one has been injured.
In these incidents, the PS Vita has overheated while charging, frying the handheld and most likely scorching the internal hardware. According to Sony, a manufacturing defect is not to blame and there are no plans for a recall. Sony believes that either liquids or foreign materials entering the charging slot seem to be the cause.
Yomiuri Online reports that the National Institue of Technology and Evaluation, a body from the Japan's Ministry of Economy, Trade and Industry, is investigating the issue.
ＰＳヴィータ焼損３１件、ソニー「欠陥でない」 [Yomiuri Online]
DISCUSSION
I used to do repairs on PSP's... People are disgusting with their handhelds. Grims, food, dirt, etc get in there all the time. I'd be more than willing to place the blame square on the user's shoulders for these failures.