What can't you do in Excel?
aneesh: Excel is actually a reasonably complete program.  That said, I would like to be able to:1. Build predictive models from data I've entered in Excel.  I find myself exporting from Excel into R a lot to satisfy this need.  Microsoft partially addresses this need with the Data Mining Add-ons for Excel.2. Have more than ~1 million rows (which is Excel 2007's limit).3. More easily clean up data in a large spreadsheet.4. Reversibly anonymize data -- if I download some logs with usernames or IPs, I don't want those in my analysis (I just hide those columns), but I do need to have a unique identifier for each row.  And later get the names back if I want.And a couple things I think Excel is great at already:1. Making data look pretty.  The charts are great, and there's (http://www.officelabs.com/projects/chartadvisor/Pages/defaul...) for non-power users.2. Making data easily portable.3. Filtering/sorting data -- VLOOKUP has saved the day so many times.