You'll find lots of good info on this at www.creditboards.com

FICO scores are interesting. More lines of credit may improve one person's credit score and may harm another's. It's dependent on many, many factors. Cancelling the cards may or may not be in your best interest (your score may be improved by keeping them open and not using them, where as it may be the opposite for someone else). There's not a blanket answer to this, but you'll find on the creditboards website that a lot of people have monitored FICO's very closely and have made info available that may help you better predict what might happen to your own score. Keep in mind the credit checks from applying for multiple cards in a short amount of time may be somewhat of a problem too.