A few more pieces of advice occurred to me since I wrote the last post.
1) Never accept counter-offers. The chances are pretty slim that the only reason you were changing jobs is money. An offer of more money or a change of titles probably won't fix all the problems which caused you to take the relatively drastic step of looking for a new job. While it's quite flattering to hear how your old company can't do without your valuable contributions, usually none of the promised changes are permanent aside from a raise in salary. Once you get used to that, and sadly it never takes as long as you'd think it would, you'll probably be dissatisfied again. What's worse is you may have burned a bridge with the company which made you an offer by accepting your old company's counter-offer. It rarely pays to burn bridges.
2) Don't go back to an old company unless you really loved it the first time. This is for much the same reasons as the point above. No matter how much a company claims to have changed, the truth of the matter is company culture rarely changes. Companies with glaring flaws usually never correct those fundamental problems.
3) Socialize with your co-workers on a regular basis. You'll be surprised at how a few lunches or the occasional happy hour can build stronger working relationships which is good for everyone involved. Keep up those relationships once you change jobs. That's the best way to build a wide network of friends. Your network can help you with finding new jobs, recommending ways to solve problems, as well as giving you someplace to do a little venting about workplace frustrations.