There’s still a lot of work to be done before Magento 2 is ready for general release, and a lot of that work will involve performance tuning. The old UI for enabling/disabling the built in profiler is gone, but this Stack Exchange answer from Marko Martinović tells you how to enable it. (a MAGE_PROFILER server environment variable with values of html, csv, etc)
Magento 2 Profiler
astorm
Frustrated by Magento? Then you’ll love
Commerce Bug,
the must have debugging extension for anyone using Magento. Whether you’re just starting out or you’re a seasoned pro, Commerce Bug will save you and your team hours everyday. Grab a copy and start working with Magento instead of against it.
Updated for Magento 2! No Frills Magento Layout is the only Magento front end book you'll ever need. Get your copy today!
Programming Quickies
Quick dispatches from the life of a working programmer.