Please feel free to ask any question here and i'll do my best to answer it but hopefully some of the other members who know a bit more will also join in and help answer some of the questions people have.
What we know so far (I think!)
1. Upgrading to newer Samsung firmware will upgrade the bootloader to knox bootloader. this will give an additional 2 lines in download mode about knox status.
2. If the Knox warranty void line says 0x1 then you cannot use knox softwareas your device has been flagged as insecure. By this i mean that if your workplace / company supports bring your own device to work for corporate emails etc and they use knox to keep security your device will not allow this. You are still able to use future samsung firmware releases with the knox flag 0x1. hope this makes sense. sorry for any confusion this has caused!
3. If the knox warranty line says 0x0 knox will work.
4. with the new knox bootloader root will work, however rooting with CFautorootwill trip the knox flag. thanks @DjeMBeY for correcting this point you can use the root method (Root de la Vega) described here for rooting a device with knox bootloader.
5. If you try to downgrade to earlier firmware / bootloader it will set the knox flag to 0x1 i.e. void.
6. once the knox flag gets set to 0x1 there is no way to set it back (that anyone has found yet anyway!)
7. some newer 4.2.2 software that's supplied with the knox bootloader has been repacked by devs to not use the new bootloader and it all works fine you can still keep up to date.
9. There seems to be a big question mark as to weather Samsung will allow hardware repairs under warranty with the knox 0x1 flag
10. only seems to affect GT-i9505 at the moment!
11. Software affected thanks to @DjeMBeY
What knox bootloader looks like in download mode . In this picture Knox warranty is in tact as the flag is 0x0:
I hope this answers some questions, anyone feel free to correct me and i'll try to keep this OP updated with info as people supply it / discover it.