Myth 8: OSS support is bad, slow, and/or non-existent
Depends who is providing it...
The positive side is that it is the customers choice. If you use a proprietary SW you usually have one source of support, whether you like it or not you have to pay. In the world of OSS you have the choice of doing it yourself (at different levels) or let someone else provide you with the support, and they are subject to competition and they know it. In my point of view competition evolves to quality and improvement.
Myth 9: OSS can’t be good because it is free of charge
Well are not all good things in life free? :-)
Seriously, OSS is not free. There is no license fee, that is the difference. There is no "free lunch", nor in the world of OSS. But the other aspects of free (eg. flexibility, freedom of choice, no lock in, etc) is an advantage for OSS.
Myth 10: Open Source is worse than proprietary software
The statement is wonderful! It means that all SW is bad and OSS worse. :-)
All recent studies says that customers that have an OSS strategy is choosing OSS because it is better.