Thanks! Shame that most of the links no longer work though.
I might go for the tea approach
Hadn't noticed that. Sorry! Well this was the most fitting one :
http://www.alleycatscratch.com/lotr/Fabric/Distressing.htm
Hooray for tea staining. As gross as it sounds, don't forget to give the armpits and lower back extra attention if you really want this to looked lived-in. I'll often cram the used teabags in those spots when tea staining to make it just a touch darker there.
For black fabric I usually water down bleach, put it in a spray bottle, and spray areas that would get the most sun (shoulders, chest, etc) to give it a sun-bleached look. If I want the parts that trail near the ground to look dirty/dusty I sprinkle them with baby powder or cornstarch (dust) or lightly spray-glue the hem and rub it on the ground in my backyard (dirt).
I use Krylon spray adhesive, which can be found at most art and/or craft stores. You know the kind you use to mount paper to mat boards for display? That stuff. I suppose you could get similar results with fabric glue that dries clear too. You'd just have to brush it on, so the coverage would probably look a bit different.
Worth noting - when you use spray adhesive on fabric it makes it nicely tacky and prone to picking up dirt, but it's not a permanent bond. If you put tons of mud on your clothes this way you'll leave a huge mess wherever you go. It works really well for just a light dusting of crud here and there. Definitely test it out before putting it on a costume you intend to wear into a home with lots of white carpeting.