Excel does have a lot of uses, but at the same time it really gets on my nerves. Not so much the program, as the idiots who use it for everything.
Some genius where I work decided shared calendars (despite having Exchange and SharePoint) are a bad thing and banned them, so departments use Excel for this and for timesheets and holiday planning and about a million other things that there are simpler and better ways to do.
Lost count of the number of "our database isn't working" calls I've had, all of which are in fact corrupt Excel spreadsheets being misused. I'm sure Excel isn't the only spreadsheet app misused in this way though.