Yes, I had 2 of my hubs reach or rather touch a 100 hub score at the same time about 8 to 10 days back. And then they slid back to 99 and then 98 a bit later.
This was after almost 9 months of hubbing. These hubs were hovering around the 95 - 99 hub score for many many weeks.
However I have no idea why it took them so long to touch a perfect score. Also a couple of hubs that were doing better even before these hubs have not touched 100.
I guess its well nigh impossible to predict the things to do to reach 100. There are no ways to craft a hub or a set formula for a perfect hub score. I can just say that write good quality hubs, get people to read your hubs and comment on them meaning get as much traffic as you can.
Other than that one can't do anything.