I hate looking for a job. It's mind-numbing, pedantic, and can be overwhelming, depressing, stressful, and agitating.Plus, as a job hunter these days, the power is with the employer. So that makes it even harder. The employer can let you go at-will (my state is at-will employment) and they can hire you at will.
Lately though, I've seen people who never saw it coming being let go from their jobs. To be honest, if you'd asked me if those people would be let go, I would have said no. That's why it's so important to always have a resume at ready, to constantly check what's out there -- even when you have no intention of looking for another job -- "just in case."
The best time to negotiate a new position is when you have one. We don't always have the luxury of picking our own timing, but if you have an inkling that things might not go as well as you'd like at your company, it's time to start writing/reviewing/updating the resume and sign-up for alerts at some job hunting sites like monster.com or careerbuilder.com.
The thing is, looking for a job is free (well, except for the time investment), and just because you're looking doesn't mean that a) you'll get an interview or b) you'll get an offer. And even if you get an interview, it doesn't mean you have to go and just because you get an offer, doesn't mean you have to accept (though I think if you get to this last step in the process, you should have a fairly good idea at the last interview as to whether you want to proceed or not; it's only fair to let the hiring manager know your interest level).
"Looking" is not a commitment to do anything. It's a step towards securing your own future and perhaps gaining a modicum of power. Okay, maybe not so much the last, but you get what I mean. I always feel better when I'm in action, like I'm doing *something* to make sure I'm taking care of me.
The employers have all the power now, so the only thing we can do is keep our eyes open and our ears to the ground and keep renewing our network, letting people know casually that you're looking or you have some interest in case they hear of something. Regardless, it's important to understand what the job market in your field looks like, to understand how qualifications may or may not be changing, and to just get out there the minute you hear a hint of trouble.
Easier said than done, I know. I've been floating on the longest river in Egypt for a while now just because. But time is ticking and since I very much prefer to be employed than not, it's time to get back out there.