Recently I have switched to Mac I currently run Yosemite 10.10.3 on a late 2013 27 inch I-mac, 32 gb memory and I work on a Cintiq 24hd. There is still a major issue with line quality in Photoshop and this time I believe it is a Photoshop-Yosemite compatibility issue and Wacom is not at fault. The issue is the notorious shoe-lace bug effect that ruins the end of pressure sensitive lines. Basically the pressure sensitivity does not smoothly taper off to zero as you lift your pen at the end of the line and instead remains at a minimal amount adding an ugly “shoe-lace” at the end of the line
This effect does not exist in PS5 however in PS6 there was a different bug in a delay between the scroll ring and scrolling. Adobe provided a White Window Workaround plugin. This Plugin solved the delay problem and re-introduced the shoe-lace bug problem.
In PS CC2014 Adobe seems to have integrated the White Window plugin into the software. They have solved the delay problem and cemented the shoe-lace problem into the software. I have tested extensively with different Wacom drivers. They are not the source of this problem. I have spoken to friends and they told me that this problem did not exist in Mavericks. It is clearly a Photoshop- Yosemite compatibility issue. For Windows users they can use Lazy Nezumi to solve this issue but it does not work for Mac. I think many artists especially Mac users who can not use Lazi Nezumi would appreciate more control over the brush smoothing settings in Photoshop. It is really high time to update the very minimal current smoothing options.
A separate Yosemite bug in Cs5 is that if you color sample the frame/ border outside the page Photoshop crashes.
Also I have noticed that PS5 brush engine is actually lightly smoother, faster and more responsive than later PS versions and is currently the best (and only) option for inking in PS on a mac because of the shoe-lace issue.
Interesting that Will Terry has also found cs5 to be smoothest: https://www.youtube.com/watch?v=ic_4YVDptXo
If you turn off smoothing the bug will disappear and instead the taper will be smooth but short (still not as nice as cs5 longer pressure sensitive taper) The problem is that then your curves will appear jagged so there is no solution as of now in CS6 and up.see this post for more on resolving line smoothing issues in PS and Wacom