Because i worked with ScreenOS for years now, and i know that JunOS will be very important for the old Netscreen (now Juniper security devices) devices. I decided to start learning this new OS.
Nice thing was that juniper created this Fast Track Program, where people with for example Cisco IOS knowledge can easy learn JunOS. Because i had done my CCNP (in july 2001) and didn't forget everything yet :). i started this Program.
First i followed the JUNOS as a Second Language eLearning course, which compared the IOS commands with the JunOS ones.
After that i learned the Operating Juniper Networks Routers in the Enterprise student courseware and lab guides. (Got a J series router at work, and build a olive).
Then i was ready for the JNCIA-ER preassessment exam. (i passed this one, so i got a voucher to take the real exame)