A Google Maps Help thread has a few business owners and consultants suggesting that Google should allow multiple Google accounts to gain access to a single business listing.
I cannot agree more. This is a feature that is currently supported in Google Webmaster Tools, but is likely needed more in the Google Local Business Listing Center. Giving businesses a way to have more than one person with access to such a listing, just makes (um) business sense. In addition, there are many search agencies that handle local listings for their clients. These agencies would love to give access to their clients, if the client needs to make changes as well.
I was going to create a poll asking if you agree, but honestly, I doubt anyone would disagree that this feature would not be useful.
Forum discussion at Google Maps Help.