Threw the High Sierra GM candidate on my 2016 15" MBP because fuck it, why not.
No issues so far! The move to Metal for the Window Server is a noticeable improvement - a lot of the UI animations that hitched on the 15" Pro's puny integrated GPU are dramatically smoother in High Sierra. The only bummer is that 10-bit HEVC playback doesn't get hardware acceleration. Skylake doesn't support it, but the Radeon Pro 460 does (and works great under Windows) - Apple just didn't bother making QuickTime use the Radeon's support, so it just software decodes it (which is very stuttery). 8-bit plays perfectly, though (since Skylake supports it).
Hopefully someone writes a macOS video player that can use the GPU for 10-bit HEVC, it'd be a bummer to have to switch to Boot Camp to watch 4K videos.
EDIT: Played around with it a bit more. GPU performance across the board seems better - guess Apple put some work in on their drivers? Under Sierra, I wasn't able to play Portal at 2880x1800 without dropping frames, but it ran under Windows at 60fps. Now it's running under macOS at 60fps at native res, too.