Sony has issued an “important notice” that shooting HD video for semi-long periods of time with the A33 and A55 may cause the sensor to overheat, shutting off the camera. How long the camera lasts depends on ambient temperature and image stabilization is enabled. If it’s 30° C (~86° F) the A55 can only go 6 minutes with IS turned on.
Here’s a chart showing the recommended amounts of time you should shoot before turning off the camera and allowing the sensor to cool down:
Perhaps that explains why other HD video-capable DSLRs have such short clip recording limits…