Do you have a T-Mobile Galaxy S II (SGH-T989) or an AT&T Skyrocket? Then you might want to check if your display is having any issues.
According to a thread on xda-developers forum, a lot of T989 and Skyrocket users are complaining about vertical lines, blobs, circles and pixellation on their displays. The defect is especially pronounced at lower brightness levels, where you can see strange vertical lines as shown above depending upon what background you have.
Not all Galaxy S II devices are having this problem, though. None of the international I9100 and Sprint Galaxy S II owners have reported any display-related issues with their phones.
If you have this problem your best bet is to get it replaced and hope the new one does not have the same problem.
Source 1 • Source 2