I'm currently helping a couple of engineering students finish a senior project that didn't get finished last year. Long story... Anyway, it's a bicycle brake tester being built for Paul Components. The mechanical design is great, but they had trouble with the electronics.
Part of those electronics involved writing numbers to a pair of Sparkfun 7-segment displays. There's a lot of discussion on the Sparkfun board about these: apparently they're difficult. I had some issues making them work ---baud rate, for example, which should be set to 9600 in setup() not 2400 as stated in some references--- but it's relatively straightforward once those issues are straightened out. Here's my code, in hopes that it'll be helpful to anyone else trying to write to several 7-segment displays simultaneously.
The serial TX line (second pin given in the SoftwareSerial declaration) should be connected to the RX pin on the corresponding Sparkfun breakout board; the RX line in the SoftwareSerial declaration should be left unconnected. I've only tested it with two boards at a time, but it should work with as many as you have room for on the Arduino. It works fine for just one display, also!