The May update to the character builder is now available (the monster tool also). I haven't loaded it yet but am doing so as I write this. I am not anticipating any problems though.
There is a lot of errata in this release - see here for the complete list. Any changes to the books of course get integrated into the CB tool, but there is a rules compendium that is being published by Wizards for release later this year. My guess is that you have to finalize your changes at some point so you can get product to the printer by a certain date so it can be shipped and released by a final date.