I change the type, in fact I use the same format that Mbaas explains in msgs #15. I liked the check box icon that he uses so much I stole the idea. I also use the dark gray color to indicate a completed action. I don't date the completed action, nor do I link or archive very much. I allow the completed actions to hang around, with their associated links, until the entire project is complete. But, I have to admit, I'm a deleter. I have experimented with a "History" or "Archive" type of thought for projects, but haven't yet seen the value. Other than a journal (also pointed out by Mbaas) I usually just delete and move on.
Out of touch for the next few days, look forward to reading more posts about GTD & PB when I get back. Really some great ideas, thanks everyone....