it's basically true. I used to have comcast, I believe my plan was 7mb down and 384kbps up. Then they suddenly came out with "power boost", and magically i was getting about what they advertised now, 12mbps/2mbps! But, after a few minutes of use at that speed it would just slowly lower back down to the rate I had before. Good job comcast, you made your service last just long enough to pass a speed test at high speeds comparable to FiOS and then slowly throttling the packets back to where it used to be 3-4 years ago BEFORE powerboost.
Since a speed boost is really only useful if you're downloading large files (since they take the longest anyway) this is really just a big pile of marketing bullshit to make comcast seem faster than it really is. Quit playing games and upgrade your shit, comcast.
It wouldn't annoy me so much if they still advertised their old speeds with "power boost" but the fact they're still doing this now is a joke. If you can get FiOS in your area, do so.