Yes, of course it is safe. The only time a ps3 is truly safe from power surges is when it is turned off. Actually it's not totally safe unless it's unplugged, a big thunderstorm could come along, lighting could make a surge in your power lines and fry everything that's plugged in.
You must never turn the switch off until the red light is on but you already know that.
The advantage to leaving computer equipment on is that it eliminates the activation surge. This is a slight power surge that always hits electric equipment, surge protector or not, when it's first turned on. When you first apply the voltage, the current always fluctuates above and below the average amperage at first. It's why light bulbs usually burn out when you flip the switch on.
The ps3 and most computers limit this effect with the standby mode. When you first flip the switch on, it doesn't activate the ps3, it only applies the power to the ps3's AC-to-DC power converter (power "supply") because it goes to standby mode first. Only a few things draw power from the "supply" when it's in standby mode, within a short time the fluctuations in the AC current stabilize so that there is much less danger from turning the ps3 on after it's been in standby mode for a bit. So for ps3's and pc's, it is nowadays generally better to turn them off. Before there were standby modes, the conventional wisdom was to leave them on though, to avoid activation surges.
The power surges are no joke. When you shut down the ps3 or pc, you should always let them sit for a few seconds before reactivating them. Flipping a switch on and off again too fast has killed many an electronic device.