In every "job advice" article I've ever read, the employee is warned NEVER to accept an offer to stay at the same job, for ANY reason at all, because the employer will no longer see the employee as "loyal".

Seems funny to me that companies expect loyalty out of us, but provide nowhere to develop. I'd have been glad staying at my past two jobs if they'd continued challenging me. Instead, they started making poor use of my time (getting me to be a data entry monkey despite years of sysadmin and software engineering experience because I was the fastest typist they knew and was "around"). They paid too much for their use of that skill, and we both knew it, and I left, and I hear mumblings and incantations to the effect that they never wanted me to leave. Well, show it.