Based upon where it is, it won't have a huge impact on the skyline, it's just not tall enough to stand out from the south, east and northeast, though from back bay, and some of Cambridge it will be quite visible. There are some great renderings on the website by the way and according to the broker I contacted last week about a unit, sales are going quite well.
This thing is only going to be in the 300 foot range (figure around 325), so like kpm said, the only place it'll have any impact will be from the west, and even then it's not much of an impact.