I recently bought (a month ago) Dell Latitude E5530 which comes pre-installed with Ubuntu 11.10. I removed Ubuntu 11.10 and installed 12.04 LTS right after the purchase. Everything worked out of box but occasionally Ubuntu completely hangs. The screen freezes and I can't even switch to other terminals by pressing (CTRL+ALT+F*). Whenever the screen freezes, CPU fan speed also increases. This is not happening when running particular applications. I mean it can hang without giving any reason or error displayed and while running any application. In short currently I can't able to reproduce system hang myself. I also want to mention that sometimes it never hangs complete day.
Here are the specs of my laptop:
Processor: Core i7-3520M CPU @ 2.90GHz
HDD: 500GB, 7200rpm (Model=ST9500423AS)
Graphics: Intel HD 4000
Operating System: Ubuntu 12.04 LTS (64-bit)