If you learn a spell via spellbook you will find a new symbol in your task bar - you have learnt this one for keeps - you can use it over and over again (as long as you have mana). It's not like on other games, where you lose a scroll after activating a spell.
And if you find a 2nd book of that kind, your spell lvl will go up by one <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" /> - so it's a good idea to search merchants for books.
