The winter months are drawing in and we are starting to get some condensation on some windows. My wife believes that as the windows are now around 10 years old the seals on the inside are getting poor as she can't remember the condensation being as bad before. The seals look okay and I think that poor seals wouldn't actually lead to condensation anyway. With the heating turned on/up the condensation disappears. Could she be right about the seals?

doubt the seals have anything to do with it as generally speaking most condensation is due to lack of ventilation - if anything, the seals being less effective, would give you more ventilation

http://www.windowstoday.co.uk/condensation.htm