I have recently switched all be reluctantly to Windows 8 and when installing WinRar, the right click context menu features, (Extract here, add to, etc....) do not show up. I clicked the settings during install and also went in to options/settings/integration tab and it was checked. I tried unchecking and restarting and rechecking with no luck. Does this feature not work with Windows 8?
If you have Windows 8 64-bit, make sure you installed WinRAR 64-bit as well. I suspect you installed the 32-bit version and the shell extension/content menu handler DLL is obviously not being loaded by the native 64-bit explorer.exe program.