What's the difference between a placemark name and a label?

Yes, that's pretty much how it works. Think of a placemark like a bookmark in your browser - a short name for something and a fast way to get there. For example, you could placemark "123 Fake Street" as "home" - and then you'd check in by sending a sms saying "@home" - and BK would know that you mean to check in at 123 Fake Street. Nobody else sees your placemark - they see that you checked in at 123 Fake Street. This is particularly useful for places you go often, or when checking in with the full location is lengthy - for example, if you had to use "123 Fake Street, Mississippi, USA" - using a placemark, you can avoid typing all that in every time.

A label is a way to describe a location, and when you use it, people will see what you called the place. So if you take "123 Fake Street" and call it "home" with a *label*, what people will see is "Matthew checked in at home (123 Fake Street)".

There are limitations to labels - you can only create a custom label for fairly precise locations, like street addresses, and they only show for fairly precise locations. If your privacy settings are set to show only the town, the label won't show up.

In summary - placemark: ease of checking in - label: a more descriptive name for a location.