I think Google Latitude is going to be very helpful in visually showing you where your friends are. Since most of your friends are already on google, it makes sense to have an integrated system where you can track the geo-location of your friends or families in real time. One of the great aspect of Latitude is the privacy setting where you choose who sees your location and how detailed.
I hate getting those constant phone calls asking you where you are, so from now on, I will just ask them to check latitude.google.com to see where I am to see my progress towards the destination on the road. If you use the mobile version of latitude, you would be able to see the traffic report with the map, so you know that your friend is stuck in traffic =)
I prefer Latitude over other check-in systems because it allows tracking in real time. Next time you are planning on meeting up with your friends, give Latitude a try. If your friends happen to be around you, Latitude can send you a notification, so it is useful for meeting up with friends who happen to be near you.
Let me know your thoughts on Google Latitude. Would you consider using it?