My S2 had a loading icon burn in within less than three months. The phone was usually in low brightness, and for apps that allow, black background with with text. My S1 had burn in of the notification bar. In both cases, the burn ins were not very noticeable, and could be seen only with the phone held at various angles our with certain coloured backgrounds. I was able to sell them at good prices.
Sent from my GT-N7000 using XDA
Favourite apps: QuickPic (gallery, setting of homescreen & lockscreen wallpaper), AppZorter (sorts apps in TouchWiz), AndRecorder (clear recording of sounds), World of Goo (mentally stimulating game), SnowDeer Web Scrapper (saves entire webpage as image), MobileOdin(flash new ROMs without sweat), Taptu (quick & elegant feed reader), Gemini App Manager (prevents apps from auto starting in rooted phones), EzPDF Reader (good range of features), MX Video Player (versatile video player).