I was playing with my iPhone 3G after I upgrade to SO 3.0 with a map. I used on old version OfflineMaps but this wont work with SO 3.0
After installing Chronus ( replacement of TimeCapsule) from Cydia/Installer to my iPhone and I back up maps cache I saw the location of the city with out of the Internet connection or data plan. This will let you back up the correct map you browsing on iPhone and you can use later offline . I replaced the MapTiles.sqlitedb file with the file I used for OfflineMaps with iPhoneBrowser. It's big file and cover all Ontario and East/North USA.
I went for ride on motorcycle and try the map on more places around the city and out of the city and work perfect. I can see all Ontario and half US and location was always perfect. It's very easy and works for me.
Link to Chronus(TimeCapsule)
TimeCapsule : databinge
I had problem to instal with Cytia/Installer but was no problems with Icy.
Let me know if this works for you. John.
The BackUup file for Maps cache is located in
var/mobile/Preferences/MapsCache and there is your forlder named with the date and time you BackUp MapsCase. Just replace the MapTiles.sqlitedb file with your file you crate for OfflineMaps. Good luck.