Well, it's horses for courses, it depends what they're doing and the risk involved - If you're managing the risk profile of a multi-billion pound/dollar investment bank on a spreadsheet which it outside all normal IT governance and has never been independently tested, is not subject to change control and source control, then when the inevitable problems may well have a big effect,

Same goes for many many uses of EUCs on a more usual scale: if it's used for inventories of office supplies in an SME, then no problem, if it's used to calculate the bonuses of sales teams, you should probably go through the normal SDLC and not let the work experience kid throw something together.

If you read that research from the UOH: http://panko.shidler.hawaii.edu/SSR/Mypapers/whatknow.htm

It shows - and we all know this - that even experienced developers make mistake in code. The problem with EUC and Excel in particular, that thos problems don't get picked up because of lack of testing and/or code review - and given the nature of Excell, that individual cells contain their own code and you can't easily see logic errors at a glance - even those good practices don't get picked up. The takeaway from that research is "Spreadsheets WILL have errors and they're hard to find" and the more complex the sheet, the more those errors will compound.