I'm just posting to note that I just made a move from a tenured position to a TT position. My reason for leaving?
1) Old job = bad location, in a state institution with financial troubles and poor leadership
2) New job = fabulous location, in a (mostly) well-run private institution with no significant financial troubles.
I made a move similar to systeme_d's (though location was not a factor) to a much more highly ranked research university. It worked out really well, but I must say the shortened tenure track made the first two years harrowing. There were no guarantees and a good bit of risk, for the reasons janewales indicates:
We hire people like you quite often, and while it is indeed typical to offer a shortened tenure clock and to pay attention to publications that came before, we also need to see new and ongoing productivity. So it's important, particularly if you're negotiating for a shorter clock, to be certain that you still have work in the pipeline and can place several things well, quite quickly. The chances are that what you needed for tenure at your current institution isn't enough for tenure at an institution that is a step up, so be realistic as you think about what it will take to get to a tenurable file at the new place, and be careful in how you frame your concerns about your previous publications-- you don't want to sound like you think you can coast.
This is excellent advice. Consider carefully whether you have what it takes to succeed at a higher level (and if possible get a second opinion from someone you respect and can trust to give a candid assessment), and as you make your decision, weigh the risks. Consider also what sort of lag times there might be for publication acceptances and appearances in your field; in mine, they can vary substantially even among the top journals and were a major factor in deciding where to submit (given that I needed results right away).