I think they have instructions on the website on how to unlock the bootloader etc. There is also a lot on how they support open source with their own OS. I think that your warranty also remains valid after you unlock the bootloader and install another OS, as long as you revert to theirs when asking for support. I can sortof understand that, as it would not be feasible to support all sorts of custom ROMs.
I agree. I have one too and I am very happy with it. I also think it does not break as easily as most other phones. I drop it all the time and it is still fine, even the screen.