I'd love to see FME using the same number formatting as your computer locale, both for data inspection purposes but mainly for authoring.
Alright, data inspection in FME is just for a quick view, but still it would be nice to have a setting in the FME Options where you could choose a decimal and thousands separator, default being the same settings as your locale. In fact I'd say you don't need this setting if you could just use the same number formatting as in the locale.
However, what I find more annoying is having to use a different comma separator when writing numbers. The decimal separator in my locale and in my numpad is a comma, every time I write a number I instinctively use a comma as I do in any other software, and then when I see a wrong parameter I have to go and look for a different key in a different side of the keyboard. And that's when you see a wrong parameter, which might not always be the case.