I rarely read the release notes because I’m in a hurry to get to the good stuff. APEX 5.0 has plenty of good stuff to get to but I want to call your attention to one release note in particular: “Deprecated Synchronous Ajax in Dynamic Actions”
Earlier this year there was an interesting thread on the APEX forums titled Synchronous requests deprecated. It points out that some browsers are now giving warnings (if you have the console open) when synchronous ajax requests are made and, more importantly, that APEX apps that use dynamic actions with Wait For Result set to
Yes will make a synchronous request.