I think something that google has begun to do, and that is incredibly valuable, is data "sources" that aren't hard coded into any particular spreadsheet, but that come from a URL or API of some kind.
I should be able to make a row of "oil prices by month since 2005" that updates on its own. Or a cell with "current value of the DOW".
There are plenty of third-party plugins that do this -- Bloomberg and Reuters have them, for example. For example, the formula for the current level of the Dow Jones Industrial average is =blp("INDU Index","LAST_PX"). The equivalent Reuters formula is something like =RtGet(".INDU","PXLAST"). At work I have a sheet which pulls in real-time prices on Treasury bonds, interest rate swaps, options, stocks, futures, mortgage-backed securities, etc. and organizes them all into nice tables and charts. It's built on the Bloomberg and Reuters APIs.
I should be able to make a row of "oil prices by month since 2005" that updates on its own. Or a cell with "current value of the DOW".