@appel1 For a while at least, the biggest overhead came from simply having the analyzer engine enabled. The second biggest source of overhead (which now may be the biggest overall) is cases where diagnostics are reported. This applies even if you have them suppressed with #pragma or [SuppressMessage].
There was ongoing work to improve the analyzer engine performance
We've gone to great lengths to make sure this project performs as well as possible, specifically to avoid situations like you describe. Some limitations which resulted in performance/memory overhead for the 1.0.0 release have been resolved for the 1.1.0 beta (using features provided by Roslyn).
Note that with the previous comment I'm not trying to say you're wrong about the experiences you've been having. I'm more trying to say if you're running into a performance problem and don't have issues getting reported (even if suppressed), then:
It's unlikely that we'll be able to quickly make a big improvement since much of the project is already "tuned"
We really care about improving the experience, so even if we can't fix it immediately we're interested in finding solutions that address your needs