Pr0n: Bing - Uncyclopedia for Pr0n. Google - Wikipedia for leet.
Barack Obama: Bing - barackobama.com. Google - same
USD to GBP: Bing - 1 USD = .61670 GBP. Google - 1 USD = .61758893 GBP
Here's the search result that should determine all:
Computer Forums: Bing - ComputerForum.com. Google - ComputerForums.org