For those who don't know, church hopping is a practice that some Christians (I don't know about other religions) do to find a new local congregation to attend. While it is sometimes necessary (for a number of reasons) to do this, sometimes folks do it only because the current church is not as exciting as it once was; there are a number of good reasons that people leave a church and move on (don't agree with Theology/practices of the church is one good one, but there are others).
The quest is usually to find a church that is to find a place with better music, a more exciting service, etc. What ends up happening is that these people (these "church hoppers") bounce from place to place to place. The types of "exciting" churches tend to do more redistributing of parishoners instead of converting.
As someone testing the job market (still) and helping to find good people in my current job, it seems that this same type of practice goes on in the IT industry. When you are interviewing a candidate, you can't get it out of your head that there is a reason why this person is moving on. Of course you can ask and you'll get some kind of sanitized response that will hint at the real, but it won't tell you the real reason. You won't know that until at least a month after you hired the person.
Interviewing a potential employer is even more like this. You can't escape the fact that if you are applying for a position that someone previously occupied that there was a reason they left. You're not sure if they were just on the quest for more money/more excitement or if they left for a really good reason and that you shouldn't even think about going there...
Sometimes I wish we could set up a blacklisted company site where people who are leaving their positions could report on why they left in medium detail (for instance, "This company is too *@%^ cheap for me... they wouldn't by me an MSDN Universal Subscription for my personal use" or "my manager Brendan Tompkins is freaking moron and shouldn't be allowed to manage developers." (BTW, apologies to Brendan for misusing his name). If I could look a company up then I could use the info to make a real decision instead of having to try to guess. Eric's questions help in this regard, but they don't solve everything)