Does Paul Pierce Owe Al Horford Money?

At the 4:36 mark of the interview embedded linked below, broadcast live from the Hawks practice facility at Philips Arena this morning on "Mayhem in the AM" Al Horford (joined by Marvin Williams) says the following in response to a question about Paul Pierce and the 2008 first-round playoff series (HT: Peachtree Hoops):

"...he owes me money. Marvin was a witness. We were at the free throw line and he was telling me that they were going to sweep us and all this and, you know, we bet and I never got anything."

Questioned as to what Pierce owes, Horford responds:

"Ten thousand."

Marvin Williams clarifies the terms of the bet:

"He bet ten thousand we wouldn't win a game."

Listening to the interview, the alacrity with which Marvin Williams (paragon of honesty and genuineness by all accounts) jumps into the conversation lends the exchange credence.

At 12:50 of the interview, the subject returns to Pierce and whether Horford and Williams have lost any respect for him. Marvin Williams says:

"Absoultely not. You know, growing up, you know, Paul Pierce was one of the guys I looked up to. At the end of the day, he's a competitor, man, he wants to win just like we want to win and it's never personal."

Specifically addressing the unpaid bet makes things personal for him, Al Horford says:

"I'm not mad at him at all. You know, I mean, he's a competitor like you said and, you know, he wants to win. He's a good player so, I mean, it's fine for him to talk. He's a vet."

My questions are thus:

1. Do players regularly make cash bets during games?
2. Do players regularly make cash bets during playoff games?
3. Do players regularly make "cash bets" during games that neither party has any intention of paying/collecting?

Listen to the interview