In email, I went from Lotus Notes, to Microsoft Outlook, to gmail. And now it is the turn of the spreadsheet: from Lotus 1-2-3, to Microsoft Excel, to Google Spreadsheets.
Excel has too many features. Even at my time at McKinsey where I built very complex spreadsheet models (mostly company valuations), I only used the very basic functions (numerical operators) to ensure that I completely understand what is going on in the model. Bugs could mean billions of dollars for my clients.
The features come at a price, on my Mac Excel 2011 has annoying delays when entering even the most basic of calculations.
The design of the Google apps have come a long way. Especially for spreadsheets, collaboration with multiple people is important. And finally, the Google spreadsheet is perfectly accessible on a mobile device.