Reddit reviews C# 5.0 All-in-One For Dummies

Comparing the table of contents for both editions (assuming it's this (2010) vs this (2013), the additions for 2013 are:

• Book 2, Chapter 11: Improving Productivity with Named and Optional Parameters
  
• Book 3, Chapter 6: Programming Dynamically!
  
• Book 3, Chapter 7: Helping Out with Interop
  
  However, 2010 seems to have an additional "Book 8" which also includes these same chapters. I'm assuming the content of those chapters are very similar if not identical.
  
  As far as I can tell, they're probably mostly identical. I would suspect that the biggest difference would be with "Book IV: A Tour of Visual Studio" in which (I'm assuming you're using Visual Studio 2013) some of the shortcuts/menus might be a bit different. Most likely for the depth the book is going in to, it won't be that much different (and if it is different, probably a quick google will help you find it).
  
  tl;dr Feel free to grab the 2010 edition. The books look nearly identical.
  
  EDIT: And just to comment on what's in there, definitely looks like it'll cover the important bits. The relatively newer stuff (LINQ, async/await, covariance) you can definitely learn online separately once you have a good grasp of the language (and Visual Studio, .NET, environment) fundamentals.

This, I'm embarrassed to say, I've been thinking of getting a new one though, I might consider primer plus now you've mentioned it. :) I'm sure I've seen that book in my Uni's library one time or something quite similar, I'll have to have a check sometime.