the example below can help you
//while your activity class should be implementing OnKeyListener like below
//public class MyActivity extends Activity implements OnKeyListener { ....}
myEditText.setOnKeyListener(this);
then by overriding the method of key listener you can sense the shift key
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
    switch (v.getId()) 
    {
    case R.id.myEditTextId:
    if(keyCode==59)//59 is shift's keycode
    //do your stuff here against pressing shift key
    break;
    }
    }
you can get android key code list here http://qdevarena.blogspot.com/2009/04/android-keycodes-list.html