23mm or 25mm tyres?

I've just ordered another pair of Continental 4 Seasons - to get me through the winter. Having punctured twice in three days - on different tyres mind - I thought it was about time I got some new boots.
I was chatting to the Continental guys at the bike show the other week who confirmed that the pros all now prefer 25mm tyres over 23mm or smaller. 
I'm old enough to remember having 18mm tyres the thought of which at 120 PSI just fill me with dread now!

So 25mm are the tyres of choice for 'a better roll' apparently.
These things tend to go around - no pun intended - and I'm sure a few years from now we'll all be told that 24mm is the optimum tyre gauge. For now its 25mm unless you, like me, refuse to conform and it's 23mm! How much difference can 2mm really make?