Can sometimes take a while. Leave your bitcoin client open and be patient, it'll show eventually.
Correct me if I'm wrong, but if I'm understanding this correctly, I have to leave my bitcoin wallet client up and running in order for it to receive payouts/payments?
Yes, but you don't have to have it running all the time, only when you are expecting a payout. I also had this issue with my slush payout and being a newbie I thought something was wrong. I opened my bitcoin client and let it run until my payment was confirmed. After that, I closed the bitcoin client.