Major changes related to 5.0.4 version:
- Upgrade script engine rewritten. Now it allows to upgrade even from 4.3.9 version (from 4.3.1 should also work theoretically).
- Major caching engine support (xCache, APC, Memcached).
- Improved gmail-style upload control.
- New section icons in tree.
- Ajax-loading sections in tree now have progress indicator.
- Improved email event configuration system.
- Optimized phrase and email event storage system.
- And much much more.
Detailed issue list here: http://tracker.in-portal.org/view_all_set.php?type=1&temporary=y&project_id=1&target_version=5.1.0