I just recently installed..... yes.... give me a drumroll..... official nonleaked os 5.0.0.411 on my Curve 8900!!! It was from the actual BlackBerry website. When you come to the software screen where it asks you to select you carrier and device, you must choose "Optus Mobile PTY Limited". There you will find the os 5.0. Download and install the os. After installing your os, restart your comp. and open DM. Once you plug your device in, it will automatically check for updates, and the screen shoud pop up showing the option to load the new os onto your device. After that, you are ready to go!
The os is pretty much like the 9700, it has the blue-ish new icons, more fonts, new ringtone profile options, and much more! I recommend that you upgrade. If you have any questions, or are having trouble loadint the os, just reply back to this thread. Thanks! I will also post my PIN (only if you have a question about loading the os) 21268DC2.