This. would never buy a guide for a Fallout game. The Vault has all the info i'll ever need, and for free. the vault has EVERYTHING in the game, with details on how to get it, bugs involving it, and notes about it.
The only strategy guides I bought outright were one for Final Fantasy X-2 (i actually got two from the same guy off ebay because the first one arrived all damaged), and the one for MGS4, which did come in handy. I also got the special edition of Demon's Souls, because I heard without the strategy guide, the game was QUITE difficult. And I would tend to agree. the strat guide for that made it so much more managable.
As for fallout, not only are the games pretty self explanatory when it comes to quests and features, but the vault literally covers *everything*.
Except it takes about a month or more for half of the game to be recorded and posted to the Vault. Guide- falliable but always there, and ready as soon as you get the game, and info that the Vault may miss for a week or more. Vault- free and lists bugs and fixes as well as what's a reference to what. I use both actually. I don't have time to go to the internet everytime my unsure how to get something or where something is.