CF10 will ship with extjs 3.x and while it is currently 3.1.x it wil most likely be the latest version of 3.4.x (as per a ticket I raised that is being looked at). As ExtJS 4.1.x is absolutely mindblowingly awesome, it would be a natural progression to eventually move to that version, but it won't happen for CF10. (sadly) - hopefully ExtJS and Sencha Touch (and a SASS or LESS compiler) both make it into CF11, making it a killer product!
ExtJS 4.0 is a million times better than jQuery for this purpose, especially with one development team building all of the components, where jQuery extensions tend to be put out by developers with random dev cylces and less predictable, so hopefully the transition will occur in the next version.
'Miserable and catastrophic' may have been a bit strong, the problems can be worked around.
I am a disapointed that we're not going to see the 3.4 version of the library with CF10.
look in /CFIDE/scripts/ajax/ext/adapter/yui/ext-yui-adapter-debug.js line 62:
isIE = !isOpera && check(/msie/),
isIE7 = isIE && check(/msie 7/),
isIE8 = isIE && check(/msie 8/),
isIE6 = isIE && !isIE7 && !isIE8,
Ext makes the assumption that if it's not IE7 and its not IE8 it must be IE6.
This is a bad assumption to make, it wouldn't take much consideration to detect IE6 using the same pattern as IE7 & IE8.
If no known / supported version is detected you just don't mark any as true, or you mark the closest version (IE8) as true.
The IE6 assumption causes an 'ext-ie6' css tag to be written to the body element which invokes IE6 based CSS adjustments, which are often erroneous.
If no IE version assumption were made and no adjustments applied IE9 would render correctly.
Depending on what you're trying to do you might never notice, if you're not doing much custom UI work using the Ext library and only using Cf tags the impact is less pronounced.
I noticed today, ext menu icons have the IE6 offset of -24px resulting in hidden icons.