FORMAT: Entertainment Magazine is a weekly publication, covering television, music, theater and film. It is 7 7/8 by 10 1/2 inches. With an average of 86 pages per issue. The amount of pages in each issue mostly depends on the content for that week. I think that their strategy is useful because they are able to balance their use of content and do not need to fill a predetermined requirement when the content may not be as substantial that week.
GRID: After looking at the layout of Entertainment Weekly, here. I saw that the margin size is 1/4 of an inch around the whole magazine. The width of the gutters are .5 inch. And the number of columns that I saw most commonly used in this publication was possibly 6. They usually only broke the margin for photos.
LAYOUT AND WHITE SPACE:
As for the layout most of their articles are about 2-3 pages, and at least three photos on the spread. I notices that their larger issues had less white space 
while their smaller issues had more white space. I think that was to add emphasis on the larger issues that they contained more content. I also liked how they separated their content by color, for the book section it would always be purple and for tv it would always be green.
After taking a closer look, I think the .25 margin guideline was more of a minimum distance and not what they actually use, which looks to be closer to a half inch at least. And the bottom margins are even wider.