Many people prefer to disable Enhanced GPS Settings, XTRA data download. This is because 3G/GPRS data connections can cost a lot, especially if you are abroad and roaming.
It seems like Samsung has left some settings turned on in the registy, for debugging purposes, and this makes really slow to get a fix without XTRA data. According to Microsoft's documentation (see GPS Intermediate Driver General Registry Settings) some features like logging can be enabled for debugging, in GPS Intermediate Driver's registry settings, which stays between the hardware and your navigation software.
My experience shows that the following steps seem to improve the time to get a GPS fix, without need to download XTRA data:
1. Go to Settings > System > Enhanced GPS and set both settings to "Disable"
2. Go to your device's registry, and see the key HKEY_LOCAL_MACHINE\System\CurrentControlSet\GPS Intermediate Driver
3. Change the following string values to nothing (don't delete them, just edit them and clear the value):
CurrentLogFile (originally \GPSID_log.txt)
OldLogFile (originally \GPSID_log.bak)
4. Soft-reset your device
5. With File Explorer, go to My Device, and delete the two GPSID_log files you see, and the file named xtra. If you don't soft-reset, you will not be able to delete some of them.
6. Check again the registry setting. Sometimes in rare cases it may revert the settings back - but that's a general WM problem.
After this, if you start your navigation software under clear sky, you can get a fix in a coulpe of minutes, without the use of XTRA, or any other data source, than pure native GPS satellites.
To digg in the registry there are many free and shareware tools available, I can recommend Total Commander CE, which has a registry plugin.
Also noticed (but this may be really subjective) that flipping the device with the back upwards, while waiting for GPS fix, improves reception a bit - it seems like the internal receiver antenna is oriented to the back of the device... but if anyohe has dissassembled the Omnia can confirm or infirm this.