Bounce rates - really depend on your market and content but 18% is really good whatever market you are in. Google.com analytics specialist Avinash Kaushik has stated: "It is really hard to get a bounce rate under 20%, anything over 35% is cause for concern, 50% (above) is worrying."
On 1,166,391 visits for the past 30 days my bounce rate is 27.67% and 34.90% are new visitors, so I'm pretty satisfied with it.
mine was over 60% and i msut work abit with it, now it has more than 40% but it's ok, i'm still working for that