What can't you do in Excel?
CatDancer: Oh my goodness, you're going to get my spreadsheet rant.  This is what frustrates me every single time I use Excel (or the Google Docs spreadsheet, for that matter).I may not be answering your question since I'm talking about usability instead of more powerful features, but I can't but imagine that there'd be a market for simple and easy to use, even if it turns out it's not going to be addressed by your particular startup...I have a table, some data that I've laid out in rows and columns.  Something simple.  How much money I've been paid on my invoices to clients, for example, one invoice per row.Then I want to sum the column, to get how much I've been paid in total.  (Yes, I'm talking about a very simple spreadsheet.  But that's my point, that something so simple is still messed up!)  So I type in a formula: =sum(C2:C10)Now I add a row, to put in another entry.  Does my sum change, to include the new row?  (C2:C11)  No, it does not.So I do not want to be saying sum(C2:C10).  I want to say, here is my simple table, and give me the sum of this column.  Which, I don't know what the language would look like, but if I named my table "invoices" maybe it would be sum(invoices.C) or sum(invoices.amount) or something.Every time someone comes out with a new spreadsheet (Excel, OpenOffice, Google Docs...) I look to see if it is easier to use.  Nope!  Everyone is too busy being compatible with the last guy.