The entire suite now sports a tabbed interface that should ease transition between CS4 applications running concurrently. Photoshop in particular gets some critical performance boosts in the form of true 64-bit compatibility and GPU acceleration to enable smoother panning and zooming.
With over a dozen major programs covering needs from web and print designers and video production, you can make your pick on what program to download (after registering on Adobe's site). The Illustrator trial weights about 1GB, Photoshop goes over 800MB, while Flash is closer to 900MB. A personal favorite, Adobe Fireworks is much lighter at around 443MB as well as Dreamweaver that is ~335MB.