In my experience, they eventually get around to paying, but it usually adds up to several months of non-payment.  I'm embarrassed to say how much they owed me at the end of the year, but they sent me a check for over half of it in February.  I'm sending them another past due statement tomorrow, because the balance has crept back up again.  If anyone is interested, email me and I'll give you the email address for the CEO.  I'm not sure if it'll help, but it can't hurt.