I have had some great experiences as well; but there have been a slight handful that just are very slow to pay. The person I am hunting down for payment now has agreed to pay me as well as paid over half of their money owed - it's just they are taking a lot longer than is acceptable.
If I knew I could have a more reliable flow of income, freelancing/contracting would be amazing.
You could always factor your receivables and let them chase in the event of non-payment. This takes you out of the accounting and finance game, but you do give up a percentage of the amount of the receivable. I know as few people who do it as they have no interest in running their accounting operations. The factor acts as an accounts payable department with the added benefit that you get your money up front and don't take the risk of non-payment. Now if the client is a high risk client it is usually reflected in the discount on the receivable that you must provide. Many non paying customers, become good paying customers when a factor is involved because they don't play games. Best part is you don't have to play bad guy, because you "sold" the receivable so it is not the actions or the responsibility of your company to enforce payment.
If I knew I could have a more reliable flow of income, freelancing/contracting would be amazing.