Fortunately, user adoption is not technology dependent (atleast not most of it). Unfortunately, most salesforce.com implementation teams make it seem so. User adoption is a Behavioral change, above anything else.
1. Learn from companies that have done that successfully
My business coach, friend and an amazing entrepreneur, Xavier Augustin (CEO - Y-Axis.com) achieved 100% adoption rate for 200 over users of salesforce.com within first 2 months. You can also use his amazing salesforce.com user adoption principles.
2. Big change starts with Tiny Habit. Similarly for any salesforce.com user adoption. See this video on how to drive tiny habits for salesforce.com user adoption.
3. Training Strategy: Always train the core focus group on salesforce.com usage before releasing to your 50 odd users. And co-share the responsibility of training those users with that core focus group. One trainer, and that too from an external implementation partner will not do the 'user adoption' magic.