Excel has low level functions for most statistical calculations. The Analysis Toolpack is an add-in for Statistical Analysis that is included with the Professional version of Excel, but it is not installed by default.
Excel has the obvious advantages that it is ubiquitous and it is familiar. The spreadsheet idiom is well-suited to the tabular display and analysis of modest data sets.
Excel is not considered reliable by many professional and academic statisticians. Versions of Excel prior to Excel 2007 (for Windows) had several well-publicized errors that went un-fixed for years. Microsoft's disinterest riled statisticians. Excel 2007 fixed some of these errors, but statisticians continue to document the shortcomings of Excel's computational accuracy, plotting, and general software model.
The more dispassionate experts acknowledge the ubiquity of Excel and view it as a tool for simple calculations. Samples of web sites and articles documenting the problems with Excel are listed below.