Definitely depends on the situation. It has come up once or twice in the current campaign and we were allowed to take 20 to accomplish it and this was sufficient.
The dwarven rogue in my high-level game maxed out Forgery, along with a couple ranks in Craft (bookbinding), so that if he needed to, he could Forge a whole book! He did it once...
He did use his Forgery skill extensively, often using it to get weapons or other items 'commissioned' for royalty.