You're right: fenders, rear rack, brake lever and cable were all about 3-4lbs. If I were looking to get this thing lighter, the cheapest immediate solution for me would be to get a lighter seatpost and handlebar. If I really wanted to get spendy, I'd change the wheelset as well. But I already have a 20lb Bike Friday.
After these last few years commuting, I've now just begun to narrow down my likes and dislikes. I've gone from mtb to folding to recumbent to 700c and back to folding. By far, my fastest commutes were with a fixed 700c, and my most comfortable on a recumbent. Yet I'm still drawn to mountain biking and was looking for a solid machine which could fold – a BF Llama is way out of my budget at this time. But I've always been intrigued by the S1 because so many of its parts are steel and it is affordable. I don't like the custom-sized front hub, but after taking a good look at it this past Sunday (we all knew Pittsburg was going to win anyway), it's not as bad as I thought, though it is very "tiny" as skyfish noted above. After some commute time this week, I'll take it on some trails over the weekend and see how it does.