In Freya (and OS X), I could rest 2 fingers on the track pad and click the mouse button to right-click. (I have a 2008 MacBookPro with the actual physical button on the trackpad).
After the upgrade to Loki, I can't right click! I've tried both the previously mentioned two-finger click AND holding Command-Click. Neither works!
If I turn on touch gestures in System Settings, the two-finger tap definitely works, but I seem to have broken it while trying to configure a custom xorg.conf file for the synaptics driver.