[simias]

Some things like indenting a large file or even searching in a huge buffer can be quite slow. For instance I just tried indenting a ~1000line C buffer and it took about 2 seconds. When dealing with very large files (hundreds of MB) some basic movement and editing commands can be quite slow. Dealing with very large TAGS file (for the linux kernel for instance) is annoyingly laggy as well.

I agree that it's not the panacea though, Emacs would benefit from using a more threaded or event-oriented programming model for many things.