Getting rid of class files in Open Resource
Eclipse often annoyingly shows .class files in the Open Resources dialog, even though you pretty much never want to open them. Typically, these files are duplicates of the .java files in the workspace, because they're found in the target directory.
I found a solution here:
Open the Navigator view (Window > Show View). Find the folder you want to ignore (i.e. target). Right click on that folder and slide down to Properties. In the Info section, check Derived. Bingo! Those files no longer show up.
This also gets rid of the selected directory in the Synchronize view, which is a much more elegant solution than filtering on a directory named target.