I used Spacemacs for a while, but switched to a custom configuration with evil, general.el, and which-key. Spacemacs was excessively slow and I also often ran into strange bugs.
I didn't get any strange bugs or slowdowns, but then I am using the `develop` branch which is going to be the upcoming .3 release. I also have a few dozen layers installed.
I would miss Spacemacs' layers way too much if I reverted to vanilla. Its integration of evil-mode is also fantastic, something I don't want or need to recreate.