Mindshow's focus is on short, ephemeral content. That said, we know that you will create some gems and want to save and share those files with friends. (Please do!) Long term, we want to support that behavior, but we cannot guarantee save file stability at this point in the product. Any save made in Alpha will eventually be deprecated by features, improvements and optimizations as we head towards public release.
Save early, save often but don't get TOO attached to your work until we say "GO!"