2) T-MOBILE USERS: You will have a problem with the T-Mobile theme that is included. You need to delete it. After you have installed the OS to your computer, go here: C:\Program Files(86)\Common Files\Research In Motion\Shared\Loader Files\9700M_v6.0.0.344_P6.6.0.50\Java (the 86 in program files is only there if you are on 64 bit windows)
Delete these files: net_rim_theme_tmobile_BlackBerry6_480x360_b.cod net_rim_theme_tmobileeu_BlackBerry6_480x360_b.cod
You can also delete them after the fact by using BBSAK. You can find a download link for BBSAK in my signature. You plug in your phone, run BBSAK, go to modify .cods, then remove .cods. Remove those either of those two, if present, and reboot your device. Problem should be solved. Again, you only have to do this if you didn't delete the .cods BEFORE installing OS 6 to your phone.
Make sure you do not delete anything but the two T-Mobile themes. If you delete net_rim_theme_BlackBerry6_480x360_b.cod you need to put it back.