Safe mode is pretty obvious. Springboard restarts and all your themes are turned off, it's just a black background. A big pop-up message which takes up most of the screen says it's in safe mode and gives you a power menu to restart/reboot etc.
Mine never goes to safe mode anymore. The only time it has is after installing a buggy app.
Ahh thanks for the info. In which case i have never had the pleasure thankfully.