When Google Chrome first came out sporting its process separation feature where each tab is in its own process, it was broadly hailed as the best thing ever. The idea was to increase stability and security.
This was during a time when Plasma Desktop was still facing a number of implementation hurdles that impacted stability. So a number of well-meaning people decided that I should be informed about this revolutionary new idea in Chrome and every component in Plasma Desktop should be put into its own process.
This was applying a solution from one problem space to another that just didn't map at all. For technical reasons it was not feasible and I offered alternatives. Still, there was a good year or so when pretty much every single day I would get at least one message from someone suggesting we redesign Plasma to be separated across different processes. Some were kinder than others, but after a while even the nicest of people sounded like fingernails on a chalkboard.
Since then we've moved on to the alternative approaches we identified well before Chrome was even available: interpreted rather than compiled code. Today we're walking with both feet into the brave new world of QML. As of Qt5 we have QML2 which brings with it scene graph based rendering that can be done in hardware where available and a runtime that makes writing beautiful interfaces that are also stable very easy. It has been a long road to this point and has involved countless dozens of bright people working hard.
In the meantime, how is that process separation in Chrome working out? Here's the conclusion of one analysis based on actually measuring things: "The [process separation] mechanism is based on a relatively dated concept, superseded by compile-time code validation techniques such as Google's own Native Client [..]
An unintended consequence of this design is that all attempts to synchronize the state between two processes are inevitably very expensive. [..] It seems that the apparent improvements in the stability of Chrome come at a very significant cost; and that unless the architecture is revised substantially, it may hinder the development of tightly-integrated and highly responsive web apps."
I don't hold quite so dim a view of process separation used in the right places as one might come away with after reading that article, but it is a cautionary tale about believing in silver bullets. Different problems are different and very few design concepts carry only benefit with no cost.