This command will take forever and ever and ever (reads against /dev/random blocks as the kernel runs out of entropy). /dev/urandom would be better but still not very fast.
I recently came across a replacement for /dev/urandom called frandom that the author claims is 10x faster on i686 hardware. Based on my own tests within a VMware Player VM, frandom can generate 150MB/s when piped to /dev/null. Tests on writing to disk were a modest 50MB/s which is about all what my laptop's disk can handle.