My feature idea: conditional formatting rules in Google Docs -- not spreadsheets, text documents. Useful for highlighting names of colleagues who are owning certain tasks in a project document, or for highlighting tags like "critical" or "completed".
Right now it's surprisingly difficult to tell the application, "find every line that starts with 'DONE' and format that line as strikethrough", or "Find every time my boss's name is mentioned and highlight it with bright colors." -- I can turn it into "==!!== NAME ==!!==" with Find & Replace, but I can't set its font size or background color and I can't enforce consistency of that rule throughout the document, which is a problem if other people are editing it and shouldn't be troubled to follow my crazy formatting whims.