What can't you do in Excel?
brent: I do not use Excel regularly and I thus am certainly not a power user.  However, I would think scripting for plots would be useful (like I do in matlab or matplotlib) for repetitive, highly configured, high quality plots with the ability to easily export them as ps or pdf.  This may very well be possible now (and I'm just ignorant), but that would be one thing that would be handy that I have not seen.