Illustrator CS4: bug hunting!
The good news: Outline Stroke
The first annoying behaviour that came into my mind was the Outline Stroke effect not working as expected when Align Stroke is set to inside or outside.
In Illustrator CS3 the Outline Stroke effect always expands strokes as centered aligned.
In Illustrator CS4 this has been fixed, meaning that Outline Stroke will respect stroke’s alignment setting.
The bad news: Blurred line under top border stroke
The second REALLY annoying behaviour that I hoped was fixed it’s also about strokes.
Since I do a lot of icons and mockups with Illustrator, I use the Pixel Preview mode to make sure objects are aligned to the pixel grid and don’t have blurred edges quite often. However, I always have to fight with a bug in Illustrator that draws a blurred line underneath the top side of a stroked object. Unfortunately this haven’t been fixed and still an issue in CS4.
This is clearly visible with squared objects: turn on Pixel Preview mode (View > Pixel Preview), draw a rectangular with any stroke and observe the blurred line on the top.