Hi Joe,
My personal experience is that latest versions of Hana have proved very reliable, especially since the introduction of the native repository with 7.x. I must state that due to my own requirements I have always gone the new "clean" instance route rather than upgraded. Before m2.4xlarge became mandatory with rev.72 for quite some time I chose this sizing over the smaller m2.2xlarge.
For me AWS is a reliable and economic provider - using spot requests with AMI's as daily backup. On occasion have I been unable to ping or login (5 times over 100 instance launches?) - simple matter of killing the current spot instance and recreating.