Been there several times with the 747-200 and 300.
The funny thing is that you expect something spectacular to happen. The IRS making a full swing or so. And if it swings over 180 degrees does it a 180 heading change or does it make a half loop or a half roll?
I tell you: It's terribly disapointing since nothing happens. The PDI (the little indicator that shows true track and IRS track deviation) makes a 180 degrees swing and that's it. The magnetic compasses are making 360's well before that and the sun is rising anywhere but in the east.
However if you decide to go down, beware. It's cold down there.