Didn't read through the comments very thoroughly, but I saw someone mentioned that companies use counter offers to get employees to stay around just long enough for them to find the replacement and then fire them.
It sounds silly. It sounds paranoid. It sounds like something out of a cheap novel. But I have done research for an executive recruiter for over two years as a side job, and the statistic he quotes me is this: "Within 6 months the person who accepts a counter-offer is gone."
The reasons are many for why that is. It's not always the sleaze bag just trying to buy uninterrupted productivity. Often, the person is like the original writer said: absolutely miserable.
Regardless never accept counter offers. Ever.