"PowerBoost" is a compression technology that gives the illusion of a temporary increase in download speeds above and beyond the tier of service. It's good for the first 10 MB or 10 secs of a download, but it's a little white lie that lets providers misrepresent their true sustained speeds.
It's not compression, they just don't enforce the cap on the first few seconds of any given connection. That means you can get up to 38Mbps (the total amount of bandwidth available on a single DOCSIS 2.0 carrier) for the first bit of the download if your node is otherwise completely unused.
at&t similarly misrepresents U-Verse speeds, in that if you are watching HD channels, it cuts into your Internet bandwidth unless you have the 10Mbps tier or lower. However, if you manage to get Internet without TV or just never watch HD channels, you won't run into that particular issue. The problem is that the total bandwidth between your house and the VRAD is currently capped at 32Mbps.
Max 18 and Max 24 are also distance limited. Some users are too far from the VRAD and only have 25Mbps between the VRAD and their house. Those folks only get one HD channel at a time and 10 Mbps Internet.
Moreover, Max 24 is significantly more expensive than Premier. Otherwise I'd probably can the Cox Internet and get U-Verse for Internet again. (I can get Internet only since I used to be a U-Verse customer, thus already hooked up to the VRAD, which happens to be next door)
And if we're talking real world speed, I usually get more than the cap speed (about 22Mbps, lately) when I'm downloading in the wee hours of the morning. I think something is broken with their Powerboost stuff.
Don't get me wrong, I'd rather have FTTH like Verizon has. I'd probably be on a nice 50/5 tier if it were available here.
