The top 1 item is VBA in Excel. If you don't have that, you can't get the power users to switch, and if the power users don't switch, you won't be successful. I've said it before and I'll say it again, this time in a mad Ballmer voice: Excel, Excel, Excel. If Linux would have a better spreadsheet option for power users, the entire financial sector would switch in a heartbeat, and the rest of the world would soon follow.
However, it turns out that it's actually hard to build something that is better than Excel. Really, really hard. Don't hold your breath waiting for this.