The Novice user can open a spreadsheet, fill it with hard keyed data, print it and save it.  If something goes wrong with a formula or macro they call the boss to report it.  Use what is provided without questioning efficiency or effectiveness.  Think they understand "most" functions.

The Beginner user adds the ability to format data, efficiently maneuver within and between open worksheets, insert formulas, troubleshoot some formula errors, utilize enhancements added by others, and suggest improvements related to performance.

The Intermediate user understands most of the functions in Excel, can nest them to create "Super Formulas", is able to debug complex formulas and simple to intermediate Macros, understands where to look when a problem surfaces, and implements improvements related to performance.

The Expert user understands all of the functions in Excel, VBA routines may be used in lieu of formulas for creating worksheet solutions.  Understands controls, event triggered macros, integrates Excel via imports, exports and VBA, is able to debug macros.  Enjoys advising others on performance issues.

The Guru can achieve most desired results in a number of ways.  Differentiates solutions based on the end user's skill level.  Maximizes performance in terms of efficiency and effectiveness.  Can create Add-in solutions for any level user.  May have authored a book(s) on all or part of Excel's features.