I have a ~1400 line Scala file which defines a class and an object. The class extends 5 traits. It uses mostly Java types. After making non-trivial changes, it takes nearly a minute for syntax analysis, inspections and error highlighting to finish, using 100% of one CPU core on a Core 2 Duo.
It's been a while since I've edited this file but I don't recall it being this slow in previous builds of the plugin.