The bug causing flickering in fullscreen has been recently marked on Wine Bugzilla as NEW: http://bugs.winehq.org/show_bug.cgi?id=29261 To help the Wine developers fix this issue, you may want to provide additional information about the problem on the bug's page. Or you can at least add yourself to to the CC List to show you are interested in getting this bug fixed.

I think the presence of the fullscreen flickering negatively affects the PlayOnMac experience.