I installed sabayon 7 E17 and had no problems, no glitches, but after reinstalling with sabayon 8, and installing E17 post-install I get some strange glitches.
While the most prominent is the log-in splash, it affects all transparancy/alpha/animation textures, video buffers in general sometimes get garbled as well(drop menues appearing garbled for a second etc.). This is how my splash looks: http://dl.dropbox.com/u/3995256/IMG_1681small.jpg
From what I could gather the driver version is the same on Sabayon 8 and Sabayon 7, xf86-video-sis-0.10.3. One difference is that the E17 versions on the 7/E17 cd are all the -9999 versions, and now I have e.g. Evas 1.1.0, but I have not been able to downgrade Evas or any other package to see if I can get it to work..
I got the exact same garbling glitch in Bodhi linux, so I suspect the -9999 packages solved it for some reason.