Keep cart products indefinitely?

[EvanGR]

Hello,

When the user adds products into their cart, there is a time period after which the cart is empty again automatically.
Where is that time period setting?
And how could I set it to never empty the cart?

Thanks

PS. Talking about registered users. But would also be nice if that worked for guests as well.
PS2. Would it make any difference if the checkout was handled by an extension like Rupostel's OPC?