My Hoya griffithii did not flower last year, when it had the previous two years.  I believe the conditions are not quite to its liking.  It resides in a north window in a room that never gets above 65°F in the winter time.  I was looking at it the other day and noticed that it had started growing again, and put out this enormous leaf that is bigger than any of the other leaves by at least a third.  I have noticed that Hoya leaves grown in the shade grow much larger than leaves grown in full sun.  I guess that it makes perfect sense; to make enough energy from the sun in less light, the leaf surface need bigger to capture that energy.  The leaf measures over 10 inches, or for my metric friends 26 centimeters in length.