As far as Samsung are concerned the latest Froyo and combined fixes should have sorted out the GPS.
It's still debatable that they sorted the lag and I told them I do not believe it did... but as their support team are still working on improving the filesystem one could easily take from this they too do not accept the lag is cured.
In reality, I suppose this will never be a final answer as some say it's fixed whilst others continue to have issues.
Personally, I upgraded to Froyo
(using Odin as Kies temporary bricked the phone) and with the JPO version installed my GPS is absolutely spot on.
For the very first time not only am I seeing multiple satellites with SNR signals below 20 but I am getting an almost instantaneous lock and the position is extremely accurate. Not only that but I can obtain satellites from within the confines of my home, something which was totally unheard of before the upgrade.
I use a variety of GPS Apps from Google Maps through to My Tracks, OS Atlas, Google Earth, GPS Compass Map and CoPilot.
Then for additional data I have GPS Test Plus and Ulysse Gizmos with finally Layar for augmented reality. All of which now makes using GPS a total breeze.
To note I have also used RyanZA's
z4root &
OCLF which have ensured the SGS is as quick and smooth as I could ever wish for.