Although Adobe released CS4 just last year, my university didn't adopt it until this year, meaning it's the software I have had to use for work.
And holy hell is it bad.

The two core programs that I use are Flash, and Photoshop. Now, I think CS3 was some fantastic software, the interface was clean and easy to access, the functionality and performance were great.
Then they released CS4 and everything went wrong.

To begin with, they redesigned the whole interface for the programs in their own style, which is an issue when it comes to any Windows software because it wastes time processing an interface that doesn't matter. My beef with the interface is that yet again, usability is sacrificed for eye-candy, this isn't MSN, knock it off!
Flash CS4 took the big hit here, they compressed the entire properties panel and filter panel into a single panel that only works horizontally, with nasty horizontal sliders, ick. You can get used to this, but it's still worse off.

Photoshop CS4 has a somewhat unnecessary new feature to rotate the canvas with OpenGL, arguably useful for maybe artists but largely of no real benefit. If you never use it, it's still there, demanding more graphical processing, oh joy...Thankfully that's about the worst Photoshop suffered.

Unfortunately, Flash CS4 is a hulking MESS of graphical and interface glitches, somehow making the same components that haven't changed since Flash 8 even worse!!

As an animator I often make use of these abilities:
-Alpha transparency
-Onion skinning
-Drawing objects, grouping, and breaking apart
-The brush and pencil tools
-Filters
They managed to fuck up ALL of these!!
I've had so many problems manipulating bitmap/raster graphics, such as objects disappearing from view entirely, objects not appearing to move despite having done so, objects not being interactable after breaking them apart. It's so bad that onion skinning can't be used properly, because even though you've hidden the layer, the onion skin frames are STILL THERE ON SCREEN.
I cannot even do basic things like use the pencil tool to draw styled lines, without CS4 slowing to a crawl, it's unbearable. Disabling Desktop Composition and setting compatibility will only do so much.

*ugh*, in a nutshell, if you try to do anything that pushes the boundaries of CS4, even things that CS3 could easily handle on the same system, all hell breaks loose. Congratulations Adobe, you've sucessfully created your very own "Millennium Edition" of your flagship software.
Take your IK-bones tool, your pseudo-3D tools, your "improved" tweens and "improved" interface, these just don't do the trick for any real animation.

Viva La CS3.