Personally I've always found the most important thing to offer negotiation is BATNA.

If your BATNA is going back to your current job, which is already decently paying and something you've made pretty easy by understanding it in depth, you're in a really good negotiating position from the start.

If your BATNA is unemployment, and you're not already wealthy, not so much. Some people find it tough to bluff that kind of thing, in which case, getting any job at all is going to do more for your future negotiating power than quibbling over the number. (I would still recommend quibbling, but only because most people won't retract the offer just because you counter these days!)