My son has been using software like this for a while now on his phone. The only problem is that to get an accurate positioning you really need to keep GPS switched on which drains the battery really fast. The other challenge is getting the police involved. My wife is a teacher and a pupil had a new iphone stolen. He had the GPS switched on and was able to track it to a local market stall where it had obviously been sold on. Unfortunately the police were not interested and when the stall holder was confronted by the parents the stall holder was un co-operative and as soon as they left he re-set the device.
Im not saying that you should not use this as it is a great idea - its just that there are some limitations to effectiveness.