I think part of it comes from Emacs running as one process, so things like Gnus that run periodically can make everything seem to freeze. Firefox does this a lo

I think part of it comes from Emacs running as one process, so things like Gnus that run periodically can make everything seem to freeze. Firefox does this a lot, as well, and it seems to be the new program that people criticize for being slow and bloated. It's not slow as such, but interface freezes (like when you move a window and stuff under it doesn't redraw) have a disproportionately large impact on how slow programs seem to users. You can do relatively heavyweight, long-running operations without people even noticing as long as you do them in the background and don't make the interface stall out.