What are the problems with using an Arduino in a production environment?
I want to know if there is anyone that has used Arduino boards in a real project? 


I have seen it being done, quite a few times.


  What are the problems that you have faced?


Pros:


quick to market;
low cost accessories;
large code base to drop from;
...


Cons:


only workable for certain applications -> high cost per mcu (vs. bare chips), no possibility of passing certification of any rigor, no respect from others / clients, ...
quite inflexible an eco-system: porting code to / from others can be problematic.
poor project management capabilities.
...


Each of those pros / cons can be addressed and may not be relevant for your particular application.