If it is raining heavily while I am in the sukkah, though I am exempt from having to stay in the sukkah, is it considered admirable to remain anyway?
Just as one is not expected to sit in a room while water leaks upon one's head, one is not expected to sit in a sukkah while it rains. Not only may one leave the sukkah under such circumstances, but one should. See Rambam, Hilchoth Sukkah, Chapter 6, Halacha 10. http://www.mechon-mamre.org/i/3606n.htm
26th of Elul, 5769 Tuesday, 15 September 2009