[nowprovision]

I've found complexity and/or/aka too many features discourage adoption, this was particular painful when a previous company I pushed to purchase Axosoft quickly abandoned it - nobody (including me eventually) could be bother using it. Hence easy to use, easy to get going, 'where 90% is intuitive' tools like Trello and Basecamp, arguably deficient in many formal project management areas, continue to attract and maintain customers. Combined with skype, hipchat or private slack for realtime communication seems to solve most of the headaches. A client recently added freshdesk to the mix too, again for 90% its intuitive.

[hooliganpete]

The simpler tools definitely encourage adoption. On a larger project I work on, we use Rally - most abominable platform I've had the displeasure of using - solely because the project manager is able to assign "points" to user stories, which translate to hours of work per story. Hence, when a dev is at x number of points, s/he's at y% capacity for that sprint. We tried Jira but without being able to assign capacity, ruled it out. I've heard good things about Basecamp...