Broken drivers. Broken build environments. Undocumented pin muxing. Undocumented power management. Undocumented everything. Proprietary, unavailable tools needed to reconfigure things. They took a half-finished, 30% functional board support package, excreted it upon the world, and hoped that Open Source Magic meant that everyone else would fix their shit. Nearly three years later, almost nothing has been fixed and the product (whose hardware is still unmatched for power efficiency among hacker SBCs) is effectively dead.
I won't put any confidence at all in Joule until I see the kind of hardware documentation and software support that an embedded system needs to actually be, y'know, embedded into things.