title: mongodb $in limit
body: <p>Was just wondering if there is a limit to Mongodb's $in function?</p>
  
  <p><a href="http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24in" rel="noreferrer">http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24in</a></p>
  
  <p>I have a collection of users (BIG) and have a smaller subset of ObjectIds stashed somewhere, and I want to select all users (collections) that are in my ObjectIds.</p>
  
  <p>Thanks</p>