Here is a little rant for your consideration:
I think that the "Must scribe into your own spellbook before you can use a spell" rule is the worst rule in the game (it certainly is the one I like the least personally). It makes found spellbooks difficult to price for the GM and it can make them worthless to the players.
I've dropped the rule from my own campaign with no perceived ill effects and it has actually been rather liberating in one way in particular:
If you go by the book, by mid levels, a Wizard has got literally thousands of gold pieces tied up in his spellbook. But what happens if he loses it?
He is completely buggered, that's what. To hedge against this possibility, he would have to make an extra copy of his spellbook which, although only half as expensive as the first copy, is still very costly.
So, the DM has 2 choices: Make sure nothing bad ever happens to the Wizard's spellbook or follow whatever would logically happen and let the chips fall where they may.
If the DM takes the second option and the Wizard becomes deprived of his spellbook, consider how it impacts his ability to play the character compared to any other class. For example, say the Wizard has 8,000GP tied up in the spellbook and a fighter in the party has 8,000GP in his +2 Greatsword. The Wizard loses his spellbook and the fighter has his Greatsword sundered.
The Wizard can not prepare a single new spell unless he has a backup spellbook or has invested one or more of his precious feats in Spell Mastery. The fighter can pick up any weapon off the battlefield and use it with probably 70%-80% of his former effectiveness until he gets a chance to replace his greatsword. Even if he has a lot of feats tied up in greatsword fighting (Weapon Focus and Specialization for example), he can buy a non-magical greatsword for 50GP or a +1 Greatsword for 2,150GP. He may not be quite as effective as he was before, but he is quite close.
The Wizard by contrast, (if going by the book rules) has to spend 1,500GP just to replace the 0 level cantrips in his spellbook.
By using the house rule that lets you use a captured spellbook by just spending the time to "understand" the spells in it, you give the Wizard a chance to set up a backup spellbook. It may not have all the spells in it that he would prefer to have, but at least it is something to limp along on if something happens to his primary book. Which means I don't feel compelled to pull punches when I'm the DM.