Even before CS4 shipped, Adobe released the entire documentation on the web. So if you have questions about a particular CS4 feature, you can go right to the source. Follow these links to the web documentation, a downloadable PDF manual, or jump right into a summary of what’s new in each CS4 application:

Photoshop CS4 — PDF (44MB) — What’s New in CS4?
InDesign CS4 — PDF (39MB) — What’s New in CS4?
Illustrator CS4 — PDF (32MB) — What’s New?
Dreamweaver CS4 — PDF (20MB) — What’s New in CS4?
Flash CS4 — PDF (16MB) — What’s New in CS4?
Fireworks CS4 — PDF (16MB) — What’s New in CS4?
Bridge CS4 — PDF (4MB) — What’s New in CS4?
Acrobat 9 Pro — PDF (24MB) — What’s New in Acrobat 9?