I don''t think it does particularly - the gold content is so low.
I have seen worn pieces but they were either "abused" or very old. I have lots of victorian pieces in 9kt that look great still. In the UK it can be very hard getting anything else unless you want to pay the mega 18k premium.
Thanks Pandora II Yes I know, I do have 18 carat and platinum but also some cheaper 9 carat rings and although not worn everyday they don''t seem to change over the years. I think it is like I read on the 24carat site that 9 carat is more brittle in that it breaks or twists but I think if the ring is not too thin it lasts and lasts. Ofcourse, the colour of it is not as good as higher carat golds but for right-hand rings for changing designs it seems to be okay.