Samza's author really opened my mind related to how useful stream process is to high performance data processing [1] and I think Samza's only bummer (for me, personally, today) is it's lack of support for non-JMV languages [2]
I totally agree! I can't wait for Martin Kleppmann's "Designing Data-Intensive Applications" to be complete. I've read the chapters available through the early release and highly recommend the book based on what I've seen so far!
http://dataintensive.net/