Good article by David Kenney at Relevant Magazine about how and when to leave a church. He challenges churchgoers to make absolutely sure they've done their part to work things out before calling it quits and moving on, just like you would with a friend or significant other:

...this is a relationship, and you don’t just back out because some days you don’t feel your needs are not being met. If things are stale, and you notice it, then you look for ways to ignite it again. If a disagreement arises, then you talk about it with leadership. (Yes, you get into the conversation--your church does not want an email explaining all its faults anymore than your boyfriend or girlfriend does.) A church body needs the same care and attention that your own relationships do. It needs active participation on your part. It means sometimes you need to spend your own money. It means coming alongside your church on the journey towards wholeness, and it means loving and meeting the needs of the other members.

There are certainly times when, for various reasons, we're called to move on to a different church. But I like Kelley's depiction of the churchgoer/church relationship as a very human one, requiring regular maintenance, commitment, and respect. If you must break off that relationship, do so with as much grace and understanding as possible.

And for a slightly different perspective, here's a short piece on when pastors decide to move on to a new church.