I've only been to Shanghai and Beijing but I would also like to know the answer to this question. I think for many Mandarin learners/travellers the question is not so much whether the locals *can* speak Mandarin it's whether in their daily life (when casually chatting with friends, family etc.) they actually use Mandarin more than their local dialect. If the local dialect is generally preferred then social events may be difficult for foreigners to get involved in and you/your friends will be constantly (but politely) asking to others to speak in Mandarin so you can follow. I guess other people may have different experiences of this phenomenon which would be interesting to hear...

I can assure you that in Ningbo the majority can speak standard mandarin excepet those senior local citizens. Even in my hometown ZhouShan(once belonged to the Ningbo City,speaking the same dialect), not so civilized as Ningbo,the majority people in my hometown can speak mandarin with few accent.