Hi All!
After reading up on the sparkfun product I became uncomfortable with the posts about how the 3.3 volt side was actually only 2.5 volts due to a resistor divider of 2 equal values (1/2 the 5.0 volts applied). From my experience when you start operating towards the lower limits of a device it will tend to become "spritual" (technical term) where sometimes it will work and sometimes it won't! A company called "Analog Devices" makes an IC called the ADG3304 which has one side that you give it your 3.3 volts and the other side the 5.0 volts. Another company called "Technological Arts" makes a model AD325V14 which takes this tiny IC and puts it on a board so it will plug in to a standard 14 pin DIP socket. The device has 4 bi-directional channels and they have other versions for upto 8 channels as well as a 4 channel open drain version. I hope this is useful to others.

Best, Ed