I've had the XXL since September and it's been great!
I got the one with the beige exterior and orange interior, and it's easy to see in poor light, and it doesn't look too grubby either.
I can comfortably pack a gripped 30D with 17-55 mounted, the 50 1.8 and either the 80-200 f2.8L or 550EX. And in the front compartment a couple of 77mm filters, batteries and CF cards. Or if I put the 550EX in the front compartment I can carry all my gear:
30D with grip
EOS 30 with grip
550EX
17-55 2.8
80-200 2.8
50 1.8
Spare batteries and CF cars, some filters too
But that's at a push, and it doesn't close sufficiently to be weather resistant.
I'd put some photos up, but my PC is broken at the moment. Jacobs has the whole range in stock, if they've got a chain near you.
I would recommend the XXL, the quality of the bag is very good, intense use since September and it's still perfect. I would lean towards the XXL anyway, since there's not really a big jump in price, and it's nice to have the extra space. The size of the bag really isn't obtrusive at all, it's a subtle, casual bag, probably why you're looking at it really!
A few other points:
I only use 2 of the dividers supplied, one to support the camera and lens, with the 50 1.8 underneath and another to keep my 80-200 or 550 seperate. This way, I can open the bag and put in or take out what I need, with the camera still strapped to my other hand. The bag comes with a plethora of different dividers of different shapes, sizes and 'degrees of bendyness'
The one gripe I have is that after a day, the strap can feel as though it's cutting into your shoulder, but swapping it to the other side is usually alright. The removable padded part that covers and area of the strap has a tendency to slide down aswell.