[chubot]

I don't have this experience -- I highly suspect NFS or another network file system.

On my system, hitting Ctrl-Shift-T inside xterm is almost instant, and that starts a bash process. Likewise for Ctrl-B C in tmux.

Bash's startup files are annoying, but you can probably pinpoint the problem with strace.

Or maybe try running:

    strace bash

vs.

    strace bash --norc --rcfile=/dev/null

However this isn't the full story because bash's startup sequence is a nightmare and neither of those is likely to be exactly what happens when you're starting a new shell.