i updated this morning, 2 week old 40Gb PS3. its been running all day, playing a little bit of downloaded content, dvd films, race driver grid while downloading two more demos, all without issues.
from what i read, if you managed to update without a problem your ps3 wont implode the next time you turn on the console, it should carry on to work, its just a few consoles (notably the older models) that seem to be prone to the problems.
the problems seem to happen straight after the update so if you have updated and are worried about the safety of your ps3, you should be alright as long as it was running after the update.