From The Vault
Comprehension is a Fallout 2, Fallout Tactics, J.E. Sawyer's Fallout Role-Playing Game and Fallout 3 Perk.
Fallout 2 and Fallout Tactics
Yes, reading can be fun. You receive twice as many skill points when reading books.
You gain one additional skill point whenever a skill book is read. However, points gained from books before selecting this perk are not doubled.
There are a total of 324 skill books in Fallout 3 (not including skill books found in DLC's). With this perk, you can potentially double the effectiveness of all 324 skill books, changing the potential skills increase of 324 to a staggering 648 skill points when all books are read! This, combined with the fact that some skill books respawn, means a potentially infinite number of skill points available (do not forget that you can not raise any skill above 100; however, gaining skill points from books means less points spent on that skill when leveling so careful character development is still wise).
Books that respawn are Big Book of Science (from Ant Researcher in Shalebridge) and U.S. Army: 30 Handy Flamethrower Recipes (from a raider using flamer in Bethesda Office East).
*Using this perk in combination with Leveling it is possible to get a 100 in every skill.