On the one hand this is good news, but on the other hand the introduction of SwiftShader is a bit of a headache. SwiftShader is a software renderer (usually slower than hardware acceleration) for computers which do not support WebGL, e.g. if their graphics card driver is ancient.
The C2 engine does this process on startup:
1. Ask for WebGL support.
2. WebGL supported: render using WebGL
3. WebGL not supported: fall back to canvas 2D
Now SwiftShader means WebGL is always "supported" - meaning even if the hardware/driver doesn't support it, it'll just use SwiftShader software rendering. So step 3 will now never happen in Chrome. If the canvas 2D is GPU accelerated that means there may be a big performance drop. However, on systems with really good CPUs, or systems that used a software rendered canvas 2D, SwiftShader might actually be faster - it uses all cores and dynamically compiles assembly code for optimal performance... but it's hard to know for sure. I would prefer to make the engine pick whichever is hardware accelerated, but there is no way to tell if SwiftShader is being used.
So Chrome 18 may be faster or it may be slower. Let me know if you notice any performance differences.