Lennart Karssen has a tip for those of you who use tramp and zsh. He observed that if zsh was running on the remote machine and he tried to open a file with Ctrl+x Ctrl+f long timeouts would occur making tramp essentially unusable.
It turns out that the problem involved the shell prompt on the remote machine and that a simple one-liner to .zshrc completely resolved the timeouts. If you’re having this problem, take a look at Karssen’s blog to see how to fix it.