Ask HN: Company credit card policy?

We're growing and I've issued company credit cards to my senior team. We've got firm spending limits on each of the cards, a CFO that keeps a close eye on everything and I trust that our team will make smart decisions about their use of company money.

All that being said, I'm curious to see how others have handled this. Aside from the "trust your employees" stuff you normally hear, I'd like to learn how other founders have handled this at their own companies.

Best practices? Worst mistakes? What else?