there are a few unique issues i face with excel beyond the stats package.
1. if you shift cells (ctrl c, ctrl v) around, delete or insert rows, you may mess up existing cell references in formulas without realizing it. your vlookups, hlookups will not change your column numbers just because you did. your vba code will not change your A1 cell references. things will blow up here in spectacular fashion.
2. if you have a massive spreadsheet with a lot of lookups, UDFs, non-static cell values (like a Bloomberg real time feed), it's not so clear which UDFs in which cells get calculated in what order. sometimes it results in #value errors, which is a million times more desirable than if there was a iferr(..., 0) or iferr(..., "") and you can't tell if there was a failure.
3. your macros will happily destroy your work if you let it by mistake (writing over formulas in the wrong sheet etc). python will generally not destroy the code it's running.
4. AUTOFORMAT will destroy, without any honor or humanity, any data if it just barely looks like it should be something else. I've had strings get converted into dates, 0s get stripped off (I think geneticists also face that same issue), all kinds of nonsense.
some of the problems I see raised here in HN (such as errors in formulas, sanity checking) are also issues in other tools like scipy, matlab. common errors in these languages are off-by-one matrix references, terminating loops prematurely (esp for numerical solutions), formulas not written correctly, brackets in the wrong place or + instead of -, typos in variable names, nan versus 0 vs na, these are things that affect excel equally.
otherwise, excel is pretty good. it's quick to prototype, it gives passable charts if all you need are passable charts. it's very good at displaying intermediate results. it's pretty ok for WSYWIG presentation, formatting, especially if you have custom reports to produce every week rather than regular ones that tex can solve. the biggest thing about excel is that everyone uses excel and if you try to send over results in a non-excel format they'll (clients or whoever) ask you to send it back in xls.
oh also... mediocre workers can produce excel sheets of passable quality. mediocre works may not even produce a single scipy script of any quality. I have seen some horrific matlab code, written by people with engineering background. i've seen one guy, in his desire to make a programming language look just like excel, write a single line for each of the 50 charts he creates and calls them Chart1, chart2, chart3, rather than use a for loop even though it's just 2 lines. it's totally bizarre.