I have 2 receivers. Delorme Earthmate USB (NOT LT one), stuck deep inside the dash (very much close to the firewall) in my Matrix and the reception is darn good. During the day, nice and clear outside, with the car inside my garage (there is a roof, and whiteboard/paint on top), it can get 5/6 sat strong. Out side the garage, it can get about 9/10 sat. If it put on top of the dash, it can get all 12 sats.
The only problem is early in the morning (5AM), it can't get any signal inside the garage (well after 5 min) and barely get a lock when I pull off the garage.
The other receiver is a new kid on the block Ayay Sir and can perform as good as the delorme unit. Look at Fusion One post regarding to that unit.