saving

Drupal 7's database layer makes use of transactions in several places. Be careful when you expect to see the results of node_save() outside of the scope of the current request. If someone accesses your website data before the transaction has been committed, the results of queries executed within are not visible. Either all queries succeed or nothing happens at all in a database transactions.

if we all backup each other's data with whatever space is available on our various hard drives, we may be able to save a lot of money and be better for the environment too.

Some really good software for both the client and the storage ends are needed to make this work well. Probably something as far as distributing the locations of encrypted backups also...