What\'s the best practice of using Twitter Bootstrap, refer to it from CDN or make a local copy on my server?
Since Bootstrap keeps evolving, I am afraid if I refer
Almost all public CDNs are pretty reliable. However, if you are worried about that fraction of the time when a CDN might be down, you can load Bootstrap from one Bootstrap CDN, and fallback to an alternative CDN in case the first one is down.
About your second concern: The links in this post are hard coded versions of bootstrap and jquery. So, even if the bootstrap and jquery libraries are constantly developed and get new features, your site will stay the same over time.