I haven't heard of any issues related to apps crashing or that type of bad stuff. I also didn't perceive much performance bump when I left ART enabled for a while (and I did notice that bump when I had ART enabled for the long haul on my prior Droid Maxx).
As mentioned, that repeat "optimization" of a subset of apps on each reboot is seemingly the only obvious issue with ART on the Turbo. It seems many of us have gone back to Dalvik for now as a resul. Since it clearly isn't firing on all cylinders yet, better to just stick to the default. That's my thinking and seemingly the thinkling of others.
I'm surprised with the optimization issue, since the Maxx worked flawlessly on ART. I'd expect it to be closer to ready for prime time (Lollipop), not farther away.