In at my fifth job in 32 years (not counting stuff in college). I stay longer at each successive job, leaving before mergers or (voluntarily) after major layoffs. In each case I moved on to a job with newer technology and more challenges that the one before.

This is both good and bad. Previously, it has shown employers that I am stable, and unlikely to leave at the drop of a hat. Now, it implies I'm inflexible or not up on the latest technology, or <&inser favorite excuse here>&. 8-)

I'm going to give you a piece of practical advice: You owe your employer your best effort, and nothing more. Programmers have become interchangeable cogs, as far as Pointy Haired managers are concerned. If you find a job that looks like it's more interesting or likely to let you learn something new, TAKE IT. You should be your primary concern, especially if you're younger (i.e. have fewer obligations).