I've been convinced for years that Google Docs loses things. I both had files vanish and have lost edits - one time I could demonstrate it with a screenshot of part of a doc that later reverted to an earlier version.

Other people at work agree with me. Google support insists we're nuts.

I only use it when other internal folks start collaborative docs, otherwise I do not trust it. Files don't randomly disappear from my local filesystem (and we test our backups).