title: Useful features to learn in boost for immediate use
body: <p>I know this could be seen as subjective off-the-cuff (thus a poor question), but bear with me.</p>
  
  <p>Boost has recently become available on the project on which I'm working, and I don't have much experience with it. Boost has so many parts and features that it's hard to know where to get started in learning it - especially since I'll be trying to learn it while making production code.</p>
  
  <p>So, I would greatly appreciate it if someone could list around 3 to 5 features which are very useful in general, every-day programming and state why they're useful.  I'm not asking you which is best, or trying to get a debate - I just want to know some good features to start learning and using immediately.  I don't need code samples either, I'll be more than happy to research how to use the features myself after I know which ones are sensible to start learning now.</p>
  
  <p>I'll accept any answer with a concise list of features that are sensible :)</p>