Just came back from the Rally (in Syracuse) and it seems to be the consensus that you replace ties at 5-6 years. My tires were made on 9/07 so I am ready to bite the bullet. Got a quote from a local, ...
I would have the tires inspected. Mine were manufactured in 06 (7 years in August), and I have them inspected when it is in for it's annual service. They said there are no concerns or reason for me to replace them this year. They have no cracks or bruising, and so far no patches or cuts. If you keep the air pressure up, pass on the tire dressing, they should be good for 7-10 years.