So I've been anticipating the release of Acid 4.0 for oh, about as long as I've been using Acid 3. And it's finally out! Hooray for everything! You should download the 27 meg demo and play with it! It promises various sexy things that I've wanted for a long, painful time such as plug-in effects automation, ASIO driver support, MIDI piano roll, and VSTi plug-in support. Not to mention there are a whole bunch of other things on the new feature list that I'm sure will impress the pants off me as well.
The main thing I worry about is stability. One of the great things about Acid is that it rarely crashes, which is fantastic because nothing makes you want to hurt adorable little animals more than losing your work. Even if it's just the last ten minutes, it's still awful. As I've learned from previous crashes throughout my computer-using career, I can do a surprising amount in ten minutes.
I'm installing it now. More as it happens.