To clarify my down-voted comment a bit: I think part of the problem is that GC tuning has become kind of a black art. It's hard to find documentation and advice to get good results. Tuning services like MySQL, Apache, Nginx is pretty straightforward; there's documentation, guides, tools and plenty of clear ways to monitor it. In my search for Ruby VM tuning, I've found only very technical guides or blog posts that involve a lot of steps, and are not focused on real-world experience.

That being said, I'd like to try this service, the guys behind it seem to really know what they are doing.