We need to test for compatibility issues with PHP 5.4RCx because it seems many ppl will upgrade their sites because of the hashing forms stuff vulnerability. It looks like we can not fully support PHP 5.2 and 5.4 at the same time so Moodle 2.0.x might get only show stopper fixes, no idea if we can fix 1.9.x issue.
We should imo fix all warnings and notices in 2.3dev.
Please create subtasks for individual issue, this is just a meta.
NOTE: please include "PHP54" tag in commit message.