Conclusion: In short, this is a major update that has a variety of new and/or improved features. Obviously the value of any of these updates is personal and you may or may not find any value with any or all of the features I've pointed out. Personally I've no clue as to why we have all of these great new features but there is still a continued delay for long-standing features that have needed enhancement since Illustrator 1.
Excerpt: Adobe Illustrator occupies a slightly odd position in its market. On the Mac, it’s the de facto choice for vector illustration, used for everything from logos to fine art. PC users have other options, though, including CorelDRAW and Xara Xtreme . To stay ahead at the high end, Illustrator added a number of unique features in CS3 and a new interface in CS4.