There aren't a boatload of updates to this version of Illustrator, just a select few interesting ones. In addition to performance boosts, Adobe has updated its tracing engine, introduced a new pattern creator tool, added variable-width strokes and the capability to apply gradients to strokes, and tweaked the interface. Toolsets can tear off the toolbar instead of just fly out, which is nice for the frequently used sets.
It looks drastically different on startup because it defaults to the same dark gray as Photoshop, but here I switched it back to the lighter setup. I'm not sure why -- maybe because it's so print-centric -- but I just feel like Illustrator should be light. Adobe has also tweaked the content of some of the panels as well as the way the tools orient. Small changes, like the addition of hex values to the picker and the expandable color spectrum are really welcome.
In some ways, though, the interface still feels a bit newbie-hostile after all these years. I'm an occasional user of the tracing, for example, and never, ever remember how to actually convert the trace to paths. To me, "Expand" means "grow" not "give me vectors."
And on the subject of tracing, the new engine feels faster than the old, and the interface is a lot more streamlined, but the results don't seem to be much better. It's always been pretty good at creating scalable or stylized vector versions of bitmaps. But it's not great at making editable-path versions. Plus, it takes a bit of advance work in Photoshop to make images amenable to tracing. And if it had an "ignore this area" option and the ability to configure it to apply higher accuracy in some areas and lower in others it would really be helpful.
I unequivocally like the variable-width stroke tool, though. It's simple to use -- just grab wherever you want the stroke to be wider or narrower and pull -- but deceptively powerful. It's a great shortcut for creating curvy, symmetrical objects, and when combined with the gradient-stroke capability has the potential to cut down the complexity of some illustrations.
The pattern editor is likewise powerful and useful, though it seems to require a lot more trial and error to get right. You take any small illustration and choose from a handful or tiling layouts and repetitions (such as 3 x 3 in a bricklike offset), and it generates a seamless tile fill. As far as I can tell, though, you can't align the tile within the object it's filling; you have to go back to the editor and tweak the spacing, with no real-time preview of what it will look like as the fill. And while working in the pattern editor isn't slow, it can get bogged down when you add stuff like gradient fills to the mix.
Like Photoshop, Illustrator incorporates Adobe's Mercury Graphics Engine (MGE) for GPU acceleration. And a lot of operations are faster, including tracing and blurs, but there's still quite a bit of waiting on traces -- enough that I'd groan when I had to wait for an accidental wrong selection to process.
If you use Illustrator as primarily a basic page-layout tool, the performance boost is a moderately compelling reason to upgrade, but not a must. For illustration, though, the few new features do add power that can help streamline your work and possibly inspire it in new directions.