I've been involved in countless Microsoft Dynamics GP implementations over the years and have come to realize that there is one little-recognized key to both a successful implementation and long term usage. That key is a champion.
By champion I don't necessarily mean a key executive sponsor, though without that you'll probably fail. I'm not referring to a strong administrator or a project manager, though they are important, too. For me, a true champion is a user who embraces the system and becomes the go-to person internally for Dynamics GP.
The ideal champion in my experience is a mid-level accounting person with a strong technology background. Occasionally it's a DBA with a passion for business. In a few lucky organizations, it's someone with prior GP experience. Generally, the best way to find the champion is to walk into a business running GP and ask who writes GP...