Hi everyone. I have a book ready to be forwarded, and I've never done this before. Its a signed copy of the Children of Hurin, and the value is around $400 USD. If I declare that value, what are my risks? Will I pay customs taxes on a certain amount?

This depends on the rules in your country. In Germany for instance there is no import duty and only reduced taxes on books.

The good thing about using Forward2Me is that when you tell them of an incoming package, you get to set the value of the item to whatever you want. They then use that value (accumulated if there are multiple items). In one particular shipment I had successfully labelled 5 pricey books with a value of £5 each for a total of £25 value, and that's what they used and I didn't have to pay any import fees (I live in Canada). If the actual values were used, I am pretty sure I would have had to pay more than $100 extra.

Of course you run the risk of not being compensated properly should anything happen to that shipment.