I think Lynda.com provides much better training for all the apps than any book. And at $20/month, it costs less than most books as well.

have you ever looked at the helpfiles of adobe? They are the best I've seen so far for computer programs, as they are very detailed and sometimes even explain some background knowledge (color seperation, etc.).
They definitely go further than explaining to somebody who already knows about it in theory, how he can achieve this with the specific adobe program.
So for Adobe-apps, I never needed an extra book so far.

Is your friend interested in Photo retouching? If so I recomend "Photoshop Lab Color" by Dan Mergulis. I also recommend the NAPP (National Association of Photoshop Professionals). They have a bimonthly magazine thats okay. www.photoshopuser.com

@Fisheye: I agree Lynda.com videos provide a great training. Unfortunately my friend has not a fast internet connection and the CDs are not so cheap.

@sebilar: Adobe Help is a great resource... but many users are simply paper-addict.

@Dan Weaver: very useful resources...