Personally, I don't think you will have problems with using voltage dividers to do
level-shifting, as long as the resistors are not too large [eg, under 5K], and
as long as the wires connecting the Arduino and XBee devices are short [eg,
under 6 inches].
BTW, Faludi's "book", as opposed to the info shown on his website, as ALL wrong.
In the book, he has no level-shifting at all, and all the figures show the XBee i/o
pins connected straight to Arduino 5V lines, but at least he mentions the XBee
must be run off 3.3V and not 5V.
Also, at least 1 figure in the book has RX and TX connected backwards.