I have the Wacom pen too and noticed it made using LR much slower. Some jerkiness and lagging that was not the case with the mouse.
I Have Yosemite, LR 5 and using A Retina iMac.
the pen worked fine with Capture One Pro 8 trial ( which was faster than LR anyway) so I'm presuming it's something to do with Lightroom rather than the hardware? I'm really hoping LR 6 fixes it!
I have tried to roll back several Wacom tablet drivers but that didn't change a thing. This issue doesn't only affect the curves adjustment but also several sliders.
However it just might be some sort of bad coding on Adobes part; as the HSL-adjustment sliders now behave as supposed to, after installing their first newly released bugfix 6.0.1 for LR CC (6). An odd thing is that general lagging and that unresponsive feeling increases when using scrubby sliders (marked in green below) as opposed to using the regular slider handle (marked in red).
Mark that there is no slowdown or unresponsiveness using the regular Apple Magic Mouse.
Let's hope for a quick fix! Running Mac OS X 10.10.3, Wacom Tablet driver 6.3.11-3 touch turned OFF ... all available related updates are installed. LR CC RAW cache set to 5 Gb and GPU-acceleration turned OFF.
Well what do you know ... this might just be a combination of buggy coding on both Adobe's and Wacom's parts.
One of the problem areas in LR CC or 6.0.1 is as said curves adjustments ... erratic behaviour and unresponsive pen action from using the Pro M tablet made me roll back various drivers, each time clearing the preferences etc. Until I found out that using the latest 6.3.11-3 driver and turning Touch input ON it actually is as instant and smooth action as you'd wish for, if you pick an adjustment point and then two-finger-click-drag.
Furthermore the general laggy and unresponsive feeling of sliders, and in particular using scrubby sliders, is gone if you choose to use touch input. Place the cursor over the desired slider or value and two-finger-click-drag or respectively three-finger-drag.
Even scrolling in grid view using touch input works as well! We just can't use the pens for now in Adobe LR CC.
Please note that in general I've been very satisfied with Wacom tablets and their performance for more than seven years. This is somewhat of a hickup that has been intruduced since OS X Yosemite in combination with newer Adobe applications. None the less it is utterly important to solve these bugs as it makes work frustrating.
Please note that Camera Raw 9.0 is not affected by these issues on my Mac, even though they have the same motor and tools as LR CC / 6.0.1.
In my opinion if you try this, this should fix the issue.
Lightroom (cc) preferences -> performance-> disable hardware acceleration.
Voila! Back to normal.
Okay, thanks for the suggestion Nitin Gupta aka LP! ... however that was one of the first solutions I tried as I wrote above on May 1st. It just doesn't change the curves and scrubby sliders bug with a Wacom tablet. At least not for me, so please consider this buggy thread using LR CC as Unsolved.