This presentation certainly convinced me not to learn or start any project in Scala:
I am no expert in compilers but the explanations Paul is giving makes it clear that some design decisions are making it difficult for the Scala compiler to improve or be performant.
I like his ideas on how to design things better and how to avoid the insanity of taking care of everything. He had good ideas on how to improve compilers but I think that it can easily apply on how we design software.
Cinq 