Yes, Yahoo will ban you if they catch on, but they don't seem to catch on like Google or MSN do. We regularly create new accounts using $100 promo codes for our new clients (totalling $130 in account), of which $80 is used for traffic to our sites ($50 to clients). Occasionally we will use domains/landing pages that have been used multiple times before, but often we use a domain that we have parked on top. More often than not we use the same computer/IP. Not once in many, many years has Yahoo blocked any of our accounts.