It is probably safe to assume that if you are looking at this book it is because you plan on using Excel for some projects, or are using it, but would like to become more of a power user; perhaps you have used Excel 2003 or 2007, or a Mac version, and would like to prepare for using 2010. It does not matter if you are new to Excel or reviewing, this book will likely not fail you. One thing that makes this book stand out is it's easy to follow instructions, it's ability to communicate with lots of full color pictures, and how it "tells the story" (for lack of better words) in both, words and pictures. What you must keep in mind is that this book is meant for those trying to master Excel, and perhaps how it can communicate with other parts of the Office Suite, but by no means is this book meant for developers (book is code free, yay!!) or those in a SharePoint environment (although understanding Excel as a stand alone tool will help in one adapting to Excel Services and other SharePoint related services). A final thing to keep in mind is that this is a book by Microsoft; which means that the end goal of the book is for the user to understand the tool, Excel, and unlike other books (such as those by Apress), will not show you tricks or provide you with ideas that non-Microsoft evangelists or developers have come across.
In Excel 2010, one of the major changes you will notice are modifications to the Microsoft Fluent Interface (or Ribbon Interface), which was introduced in Office 2007, and has now been "improved". Microsoft has also listened to users and has improved on format, functions, and how data is presented. Excel is one of those products that Microsoft will more than likely never completely redesign, but will rather continue to build on; therefore, whatever you learn with this book, will help you in the long run.
I'm not new to Excel, but purchased this book to prepare for a class I have participated to teach, and not only have I learned how to effectively teach Excel to beginners, but have also managed to learn a few tricks myself. Excel is one of the best products developed by Microsoft, and used across all industries, so regardless or previous knowledge, as long as you know how to use a mouse, keyboard and own a version of Office 2010, this book will greatly help.