Just in case you find your self creating or rebuilding an MDADM array here is a simple combination that will output every two seconds the status of the array. We combine watch and cat retrieve and update the status of the array.
watch cat /proc/mdstat
Every 2.0s: cat /proc/mdstat Tue Mar 5 00:34:35 2013
Personalities : [raid1]
md1 : active raid1 sdc1[1] sdb1[0]
262011712 blocks super 1.2 [2/2] [UU]
[>………………..] resync = 3.1% (8126080/262011712) finish=20.7min
speed=204065K/sec
unused devices: