I think that the largest problem with broadband and doing your own traffic shaping right now is what you lose when you do it.
For example, my Comcast cable is rated at 20 Mbit, but I often get more. A LOT more. Downloads from CDNs that have local servers can reach 45 Mbit in bursts. I don't have really reliable bandwidth tracking, so that number could be off, but 45 is what I've seen.
If I use standard traffic shaping I'm limiting my speeds to 20 Mbit when I might have the option of twice that speed.