They seem to last quite a while. According to the service records, the front shocks on my old '09 were replaced around 80k miles while the rears were untouched at almost 150k miles. That one doesn't ride as well as my '07 with 118k miles, but I think it's because it doesn't have air suspension in the rear. If you ever have a fault, they default to being really stiff and they were clearly working. The one's on my '07 show no evidence of being changed. The non-AD suspension rides and handles noticeably worse.