I don't know if there's anything online, but I evaluate the level of proficiency based on what a person can do in various Microsoft applications. People basically fall into a Beginner, Intermediate, or Proficient/Expert user level.
For example, in Word, a Beginner is someone who can create a document and do basic formatting. Intermediate users should be able to insert page breaks, create headers/footers, and insert graphics. An Expert can create automatically generated tables of contents and merge form letters from a database of addresses (usually in Excel).
In Excel, Beginners can create a basic spreadsheet with tables of information and format it for printing. Intermediate users should be able to create auto-calculating spreadsheets, draw pictures, and sort and filter tables of data. An Expert, should be able to create pivot tables, write macros, and link Excel spreasheets.