In reply to laurenmcginley:
Most runners will suffer from various niggles, particularly us 'more' mature types. I'm unconvinced that it's primarily due to 'worn out' trainers, and (IMHO) is usually due to upping mileages too quickly, doing lots of hills or muscle weakness (and been too lazy to keep upwith remedial exercises).
Also changeing running styles or switching to shoes with different drops also puts stresses in different areas. Road shoes can begin to feel harsh as they wear out, but it's not so noticible if you do most of your running off road.
Looking at the replies above, most runners are more worried about the uppers falling to bits rather than injuries (inov 8 aren't unique in this), apart from waitout, who seems to be heavy on the soles.