Maybe I'm missing something .. what's to stop me from buying reserved instances for the smallest instance within a class and then assigning these to the largest instances in a class?
If anyone else knows, that'd be helpful - I'm thinking of just buying a ton of *.smalls...
// Edit: Oops, maybe I misunderstood the parent. Sibling's right; you'd need 256 small RIs to make up for one 32xlarge RI. I'm wondering why we should ever buy 32xlarge RIs and lose granularity.
The bigger win, for me, is the AZ flex, as it is a pain to manage multi-AZ setups.