I played with it for the first time last night and it is really easy to use.
The library includes transmitter and receiver examples. I just compiled the two pieces and loaded each on a separate Arduino and it just worked. I'm using the 434Mhz transmitter and receiver that I got from SparkFun.
The only issue I ran into was that the examples would not compile without adding the statement
#include <WProgram.h>
above the #include statement for VirtualWire.h.