It is thought that Shakespeare borrowed the title from the Epistle Directorie to the Gentlemen Readers by Lodge. Referring to his novel Lode writes if you like it, so. Shakespeare changed the title to As You Like It because that has more charm. Also, the saying As You Like It implies the freedom of thought and indefference to censure that the characters express throughout the play. Another line of thought is that Shakespeare did not have a title for the play. It was named As You Like It meaning that the audience could title it and think of it as they wished.
Source: http://books.google.com/books?id=cHD3DHyvAPAC&pg=PA6&lpg=PA6&dq=significance+title+as+you+like+it&source=bl&ots=53s2zySyL8&sig=MebpYfr7NPqNonzzQnKemB3oi_0&hl=en&ei=Ut_1S8nEH4uCswP-tMyHBQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CEIQ6AEwBw#v=onepage&q&f=false (Pages 5-6)