And some people have this funny belief that true freedom applies to everybody. If I write code under a free license then everyone should be free to do with it as they will, no restrictions. Otherwise it isn't free: in "protection from" Vs. "freedom to" the freer one is the one with the word "free" in it. Doesn't seem so hard to understand to me.

In-memory data storage is fine as long as it isn't primary data storage. Yes it's faster but there are a lot of downsides as well. The most important is that it isn't easy to share between servers (a close second is that it's hard to replicate to a remote site for disaster recovery purposes) so each server needs to have its own copy of the data and there needs to be some way of keeping all that data in sync.

The alternative is to have good old "traditional" storage sitting where it always sits and when the servers boot up or start their processing they load in the appropriate data set from the storage in to memory. This gives you all of the benefits of the fast in-memory processing without worrying about all of the downsides you create by using it as primary storage. So the memory isn't storage, it's cache.

So the real battle that will take place is not between hard disks and memory, it will be between RAM and SSDs.

No, the basic rules are:
      - Don't post sensitive user data on public sites

The rest is damage limitation.