I read that Wunderkind has added some new functionality to the popular Wunderlist task manager tool (they report more than 5 million users now). Obviously they also decided that it was time to start making some money so the new features require signing up for a pro account:
Along with file attachments, they are offering task sharing, unlimited subtasks (otherwise limited to 25), and a broader set of backgrounds. Recently the company added tags to the mix.
Personally I think file attachments, task sharing, and subtasks are part of the minimum subset of functionality for team task management tools (see Setting the bar for team task management apps), but you have draw the line somewhere to make money.