YUI 3.4.1 PR1 is now available for community testing and feedback. It is available on the Yahoo! CDN at http://yui.yahooapis.com/3.4.1pr1/build/yui/yui-min.js, and you can see the changes going into 3.4.1 from the list of tickets checked in for the release.
The 3.4.1 release will be a smaller bug-fix release with a shortened development cycle, scheduled for go-live by October 5th. Please file bugs and regressions in the ticket database on YUILibrary.com by the morning of Monday, September 26th so we can make sure any critical issues are addressed before the general release. If no urgent issues are reported, we will release 3.4.1 as early as September 27th.