The Java version of Google Maps does not run properly on the Samsung BlackJack (as well as other Windows devices). Fortunately, Google has now released a native Windows Mobile version of Google Maps, and it works perfectly on the BlackJack. To download it, go to
http://www.google.com/gmm on your Windows Mobile web browser, and just download the CAB file.
UPDATE: After making this post I discovered a really nice Google Maps feature. Once Google Maps is installed a new menu option is added to the Contacts application. Select any contact, and you'll be able to select "Locate In Google Maps" to do just that. Very cool!
It is possible (just) to get google maps to work on a windows mobile device - but it's very, very painful... involves installing a different JVM, and then manually editing classpaths... with a stylus... and its soooo slooooowwww...
This seems to work really well - and at a useable speed even over GPRS.
It does tate when you go to install it that its only for the US / Australia etc., but it seems to work fine for uk as well - although the find a business functionality dooesn't seem to work at all...
Finally... a useable mobile mapping application :)