I was wondering if the effect of reading a skill book only lasts for a certain period, cos the game always says the skill book expires. I thought it should be a permanent upgrade like in FO and FO2.

Books are permanent, you read a mag which is temporary. There are a lot of mags to find and not many books.

Oh, yeah, i should be referring to Mag. Thanks for the info. It's just that past FO does not distinguish between effect of a book and a magazine. I'm completely lost.

You'll find a total of around 4 books per skill, except Explosives which only has 3. Each book that you read permanently increases a skill by 3 or 4 with the Comprehension perk.

Skill BOOKS give a permanent +3 to the appropriate skill. Skill MAGAZINES give a temporary +10 to the appropriate skill. That's the easy way to tell them apart. Plus the books are all the same ones as they were in Fallout 3, plus the Wasteland Survival Guide (for Survival skill naturally). The magazines are all new, and you will find a lot more magazines than books. They are best saved until right before you need a quick boost in a skill.

Certain perks will increase the effectiveness or time of effect for books and magazines.