I have a Samsung Fascinate, model SCH-I500. I have noticed lately that it takes a really loooooong time to acquire a GPS signal when using Navigation, sometimes over 10 minutes. I live in metro Atlanta, so it's not like I am out in the sticks somewhere. It's gotten so bad that if I am going somewhere, I'll start Navigation up 10 or 15 minutes before I leave so I can have a signal before I depart for my destination. Sometimes, if I am not going far, I will just sign on to my computer and print off a map from Google Maps because by the time my phone acquires a signal, I could be at my destination.
Don't know if the problem is my phone (it's 3 years old) or something else.