I noticed that i was seeing smudged and distorted icons in Alt+Tab Application / Task Switcher in GNOME 3.6/ openSUSE 12.3. I also noticed that this condition appeared and disappeared from time to time. I failed to understand as to what was is causing this problem.
Image showing smudged icons in Alt+Tab switcher
After a few days i noticed that whenever i refreshed my GNOME desktop this issue disappeared. I confirmed that the solution does fix the issue issue by restarting my OS and i found that refreshing GNOME, indeed helps in banishing the smudged icons. Hope they fix this in GNOME 3.8.
Alt+F2 followed by running the command 'r'
Alt+Tab switcher looks good after desktop refresh :-)