Hi Avenue 33,
Thanks for the response and on further reading, I figured it out. I forgot to manually add the libraries I wanted to use to the makefile. In retrospect, I understand why the makers of xCode configured the system that way (i.e. you have to explicitly list the libraries, making it more difficult to select the wrong one inadvertently) but this adds to the steep learning curve for folk who are new to xCode. After all, the Arduino IDE doesn't feature a makefile modification requirement, though at the risk of duplicate Libraries potentially confusing the user or the compiler.
For anyone considering EmbeddedXCode:
Despite the steep learning curve, the xCode environment is truly a huge step up in terms of its functionality over the Arduino IDE. If you are a Mac user, definitely try it out. While dealing with some of the plumbing can be annoying and vexing at times, the ease with which one can code is impressive.
Some day, I may even use some of the more sophisticated features such as external debugging (good luck!) but I figure there is plenty of work ahead integrating my various efforts into a coherent set of libraries that can then be leveraged. xCode makes that effort much easier.
EmbeddedXCode enables us to leverage the xCode IDE across a plethora of platforms, including Diligent, Maple, AVR, mbed, Spark, etc (the list is impressive!) Thus, you can explore far more platforms with the help of embeddedXCode while only having to learn one IDE. That alone is worth a great deal and the Hobbyist pricing is more than fair.
Thank you, Avenue 33!