How many (and where) were security gates added after 9/11? I can't think of that much in way of layout changes anywhere I regularly was in Europe around then.

And having grown up in the UK, this was essentially my normal experience (albeit mostly at EDI). What I remember is changes (sharps, etc.), but nothing so radical. France and Germany were the places I was most often flying to and I don't remember much on that side either.

In a sense, this is all unsurprising: terrorism had been viewed as a risk in several places in Europe for a long time prior.

I recall the big change in the US (particularly PHL) after 9/11 was that you needed a ticket to get to the gate; before that my parents would meet me at the gate when I was arriving. Taking shoes off and the liquids ban was substantially post-9/11, if I remember correctly.