* Nearly no security from serious chainsplit attacks in SC (yet?) - too low difficulty
* Far too fast block timing - after all you still have to wait ~1 hour to be sure, no matter if it takes 6 10 minute blocks or 60 1 minute blocks, they are equivalent from a security point of view
* Most of the interface stuff can be anyways ported to the bitcoin client too (which also has a great QT interface in the pipeline)
* Fast difficulty re-targeting can cause huge spikes in difficulty and might lead to even more pump 'n' dump (or on-off mining like namecoin)