Load averages are exponentially damped averages which reflect the run queue of the processors. Or, the number of processes waiting for CPU time. On Linux, I believe it also includes blocking I/O.
For instance, my CentOS server has two processors. I can comfortably have load averages of 4 or 5 before I need to start worrying. In DD-WRTs case, getting to 1 is okay, but unless it's really heavy load, you might need to look into it.