Using Microsoft's Application Blocks

I haven't done a lot of .NET programming, but I've examined a few of the application blocks published by Microsoft's Patterns and Practices group. I was wondering how these are typically used:

• Linked directly into applications
• Source added into applications and built with them, perhaps with some customization's
• Sample code used as reference while writing application-specific code

I'm sure all three of these usages are common, but what are the most typical usage patterns?

Are there a few particular application blocks that are used by "everyone?"

Note: This question is related to, but not the same as Enterprise Library Application Blocks OR Home Grown Framework?.

I usually put the source into my project, and then I can get better intellisense (and a better understanding of them). I don't tend to customize them at all though. I like to have them stock so I can just distribute the stock binaries anytime I need them.