This is what I experience, share this out with you all, hope that it will help.
Samsung Galaxy S- I9000
Firmware: Froyo XWJPA
Lagfix: No RFS Advance, ext4
What I tried
1. Use Titanium Backup to force remove - Failed
2. Use Terminal Emulator to enter "su", follow by "pm uninstall com.google.android.apps.maps" - Failed
3. try "adb remount" - Failed
with the help from my friend, I did the following steps and it works
1. Install root explorer (Android Mate I installed, it's also a launcher I believe)
2. Under Android Mate > Apps Manager > System , you will find "Maps" is there
3. Go Android Mate > File Explorer >
a. default level "/mnt/sdcard"
b. go 2 level up to "/"
c. select "system" > " app" , the director will be now "/system/app",
d. remove Maps (make a copy to other folder just in case you need it back and DELETE Maps under "/system")
4. Go to Android Mate > App Manager > System, remove/uninstall Maps
5. used MarketAccess, selected T-Mobile US, Go to market to install Google Maps (or use the Maps.apk attachment in this post)
7. Go to Android Mate > App Manager > you will now see Maps appear under "Download" instead of "System"
8. Uninstall the Maps from "Download"
10. Install brut maps (the 1st download in option 1)
reboot, should work fine now.
Hopes the info above helps.
You can have Android Mate uninstall after the installation successful