I buy & download a game from PSN on my user account on PS3 #1. Then I switch to PS3 #2 and login with the same PSN account. Can I download the same game without paying twice?
Yes! Just go to your download list and redownload it on your PS3 #2.
Since November 18th, PlayStation restrict sharing from 5 devices down to 2.
Yes, but the maximum number of devices (PS3 or PSP) that can share the same PSN account is five.