Drag and Drop in Trello
Where Trello's real strength as a project organiser comes into its own is in the way it allows you to pick up and drag any item from one board to another, making it a breeze to move something you need to do right away to 'Urgent' or from 'Ideas' to your current project or however you've got your system set up. The whole item will move, complete with images, checklists etc. You can even move items from one collection to another although you have to drill down to the option.
Which Visual Project Organiser - Trello or Springpad?
Both Trello and Springpad both have such a robust set of features - many of which there simply isn't time to cover here - that it's truly difficult to decide between them or say that one is better than the other. In the end, since they are both free, I suggest you try them both and see which works better with your workflow.
Ask yourself: What complex creative project have I got in hand right now that could benefit from the use of a visual project manager?
Read: Springpad v Trello - part 1 and a 'Tour' of Trello
Share in the comments: Have you tried Trello or Springpad? Which do you find most appealing for your workflow as an artist?