Be warned if you are using the trunk code because it may introduce new changes like this that may break your code completely. You may switch to 1.0 branch if you are working on some big project that needs more stable codebase.
I thought branches/1.0 was the developement branch and that you were merging to trunk from this branch when all was considered stable
So if I understand right :
I f I have a custom attribute that I want to be massively assigned I need to declare it in rules() with an actual rule of the 'safe' rule if I don't want it to be validated
Yes, you are right. The 'safe' rule is designed for this purpose. Combining with 'unsafe' rule, the new safe attribute scheme should be able to implement the old safeAttributes() scheme.