1.) mx namespace is now changed from

xmlns:mx="library://ns.adobe.com/flex/halo"

to

xmlns:mx="library://ns.adobe.com/flex/mx"

2.) Border is now called BorderContainer

... more to come I'm sure

3.) The new flash builder or flex or actionscript api or sdk or langref or whatever Adobe calls it today is at

http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/class-summary.html

4.) The property baseColor on a button and other components is called chromeColor now

5.) Access from within a itemrenderer of the dataprovider seems to have two scenarios

A.) A List s the base allows you to say

for each (var xmlNode:XML in (parentDocument.parent).dataProvider)

B.) If using datagroup then use

for each (var xmlNode:XML in (parent as DataGroup).dataProvider)

6.) Another issue has be one with DataGrid throwing errors about sizing and layout

The errors were pointing to line 3325 contentwidth properties. The issue was caused for a few reasons and we saw different errors. It had to do with unrelated skins used elsewhere. TextBase seemed to be the root of a lot of errors and we used mx:text or better even spark label. After doing this the DataGrid seemed to stop throwing the errors. This is still ongoing a bit, but beware of using s:TextBase because it has somehow changed.