- Technically - As in the Bitcoin client, the operation of the system, mining, security, etc.
- Culturally - As in mainstream acceptance, user and merchant adoption, Bitcoin's image (or image problem), etc.
- Practicality - As in the practical uses and difficulties in Bitcoin (a good example would be people who worry over wait times for confirmations).
There's no need to limit your answers to one per category; feel free to pose as many as you like for each category or post answers to just one or two of them. Your answers can be as detailed or straightforward as you please.
Thanks, and I look forward to reading your responses!
Technically - the ever increasing size of the blockchain; risk of opportunistic behavior by someone like Ghash.io - not saying Ghash is bad just that they could engage (or were close to being able to engage) in exploitive behavior; possibly not enough coins
Culturally - regulation and how new users are such easy scam targets; confusion over too many alt coins
I think we are past bitcoin's image problem.