Facebook application specifically for iPhones just launched the Facebook Places feature where you can log in to Facebook and check-i. Twitter also initiated to include a location feature a few months back.
With this upgrade in Facebook mobile app, you can actually “Check In” and announce your physical location to your Facebook friends. Your Facebook friends then can tag you as being with them. You also have the option to un-tag yourself.
The only implication of this in a safe-sense way is that you will actually be announcing where you are to all your Facebook friends. Unless all your Facebook friends are really your off-line friends then it would be no problem. People just needs to be careful because with this, you are now highly stalkable.