Many people still save their data into Microsoft Excel files. This is an unhappy choice for many reasons but many was already written about this topic. Furthermore, unfortunately Excel become a de facto standard in many business environment and this routine seems to be difficult to strike out.
Many solutions have been implemented to read Excel files from R: each one has advantages and disadvantages, so an universal solution is not available. Get an overview of all the solutions, allows the choice of the best solution case-by-case.