I got the dirty great big RoseBikes catalogue the other week, and browsing through, came across this frame bag for £11:
http://www.rosebikes.co.uk/article/xtre ... aid:142456
I'd been looking at getting a full frame bag, then a tangle bag type thing as a full frame was more than I could justify, then thought, for £11 it's worth a go rather than a tangle bag (as i'm on a budget).
Here it is on my 29er Inbred:

Pros:
Cheap
Seemed reasonably stable (without too much weight in it)
Didn't catch my legs on it during general cycling (although did brush it a few times during energetic throwing around of the bike, but nothing serious)
Can still get bottles in the 2 cages (although see cons below too)
Cons:
Not the largest bag ever (I had a Topeak Mountain Morph, 2 large rolls, bag of crisps, large bag of jerky and a large bag of Skittles in it in the photo and it was full)
Probably not waterproof (not tested though)
You can get a bottle in the downtube cage, but can't use it while riding as you have to shove the bag out the way to get it in and out (although a side entry cage would solve this)
Summary:
Not nearly as much storage room as a full frame bag, or even a tangle type bag, but almost too cheap not to try one if you're looking for a little bit more on bike storage but don't want to spend much. I've not had a Jandd bag, but from photos it looks pretty similar, but is cheaper than the Jandd and won't attract any import duty.
Last bivi trip I had a 5ltrs bag on the bars, 5ltr bag under the saddle and a 25ltr pack. I'm hoping this bag will take a few bits (maybe my food) out of the back pack to lighten the load on my back.