I seriously hate the Galaxy S for it's GPS. I mean really hate. Although having improved the fixing with newer firmwares, it is still atrocious while navigating: skipping all over the place and giving wrong directions and above certain speeds (around 140-160Km/h) loses gps altogether.
For me its basically unusable and I was very close to throwing it out of my car window a lot of the time!
Luckily I still had my Holux GPSlim 236 from the times were integrated GPS was still a myth and alongside Bluetooth GPS Provider it works like a charm. Pinpoint accuracy all the time. Finally my Galaxy S feels like my Milestone did GPS-wise.
Of course it is not practical to carry around a GPS receiver all the time, but for those reliant on in-car navigation it's a good solution as gps receivers should be pretty cheap now.
For anyone interested I recommend a Sirf based chip as the app support NMEA.