unity 3 vs unity 4

I wish to enter desktop game development with Unity. I notice that the most recent version of Unity is 4.0.1 but in the book market I can only find books on Unity 3. So I am wondering whether there are big changes made by this updating and whether it is appropriate to start to learn from a Unity 3 book.

Learning from a Unity3d 3.0 Book is not wrong at all. Most of Base of Unity3d remains the same. i myself learned using Unity3d 3.0 book. Just for your info Some of new changes in Unity3d 4 from 3 are as follows:

  1. Mecanim
  2. Real- Time shadows for all platforms
  3. Direct 11 Support
  4. New Particle System - Shuriken
  5. Dyanmic fonts
  6. Adobe Flash / Linux Support
  7. New GUI System(coming in 4.x series)

Some of the best books to get you started as begineer with unity3d are:

Unity3d 3.x Game Development Essentials from Will Goldstone
http://www.amazon.com/Unity-3-x-Game-Development-Essentials/dp/1849691444/ref=sr_1_sc_1?ie=UTF8&qid=1360866214&sr=8-1-spell&keywords=willgoldstone

Holistic Game Development With Unity
http://www.amazon.com/Holistic-Game-Development-Unity-All-/dp/0240819330/ref=sr_1_2?s=books&ie=UTF8&qid=1360866407&sr=1-2&keywords=unity+3d

Also video tutorials for beginners from will goldstone
http://www.youtube.com/watch?v=pgEwA_XnoH8

unitycookie.com also has lots of good video tutorials for Unity3d

In short you can use unity3d 3.0 book for learning unity3d 4.0

My opinion is to always stick with latest technologies. This does not mean that a book for Unity 3 won’t help you for version 4. The interface is the same with few minor changes and thus you can follow any Unity 3 tutorials