I am using Helios on Mac Snow Leopard. I don\'t know why but all of a sudden my arrow keys and delete button start not working only on Eclipse (so Eclipse ignores them) but
I had the same problem with the "Delete" key in Eclipse 3.7.0 on Windows Vista. Suddenly the key stopped working and I couldn't figure out why. Recently I found a way to fix it when the problem occurs - it works for me every time:
In a code editor window in Eclipse, hoover on some method or variable or what have you, until the popup window appears with "Press 'F2' for focus" in the lower right corner. Click the popup window to switch focus, then click the editor window again so the pop-up disappears, and voilà, the Delete key works again.