For me, the ones that I've found most immediately useful are the performance enhancement centric tags like cfthread. Having an event based framework that was unable to spawn threads was always a problem. Now every event can be launched into a thread where the processing is done in parallel. Just as it should be :-)
Threading is the one single thing that has the capability to make the responsiveness of ColdFusion sites legendary.
Other things that have caught my eye and I'm tinkering with are the cfpresentation capabilities and improved PDF functions.
On the AJAX side of things, I haven't had a client as yet that really needs it for their site to be workable so I can't really say. It looks cool though.
The cfexchange and cfpdf functionality have opened up new areas of development for me that I have struggled with or waited on for a long time. With these, Adobe has made certain projects I have worked on for years MUCH easier.
Additionally the performance enhancements were a huge welcome. To see the memory usage decrease so much and the speed of existing websites instantly improve was very satisfying.
Where to start....I guess for me I'd go with cftextarea with the integration of FCKEditor/ricktext (which I heavily use in an app I developed). The AJAX is great and my co-worker and I are starting to enhance our applications with Spry.
"This is NOT a message from Adobe! Where did Nick get that erroneous information?
Some Indian CF dev posted it on LinkedIn (quoted exactly as above) as a message from Adobe so maybe Nick got it from there and wasn't paying attention?
"So the answer when Adobe would dump ColdFusion the same way they did Fireworks last week, Flash last year and progressively every otherproduct they got from Macromedia - is soon.
When will they get to the last man standing - Dreamweaver or is Muse…"
Dear members, please find below a message from Adobe,==In an effort to assist the ColdFusion community, Adobe, and the larger open source world, a few leaders in the ColdFusion arena have stepped forward to form an open source software development group known as 'Team CF Advance'. The primary purpose of this development group will be to advance ColdFusion applications as an open source solution through development and improvement of open source software solutions combined with social marketing…See More