Not worth the risk. While the micro instances can handle the load and have good burst performance, they aren't good if the load is sustained. So if you get a sudden burst, and load average jumps, expect EC2 to penalize you.

See steal time and stolen CPU - http://www.newvem.com/whats-cpu-steal-time.

I have seen a micro instance become unaccessible to even ssh after a prolonged activity.