I know what youre talking about, n_a_nutshell. It's because of the scroll in your mouse. I don't know how exactly it works, but I came across bigger fonts in G too. It's not Google, it's your mouse.
as you probably know you can change font size in the view menu of IE (view > text size) i've confused myself a couple of times by changing it and forgetting i'd done so - but thats because i'm a bit thick.
LoL This happened late last night. I guess I was getting trigger happy while pressing and unpressing the crtl key to block and allow pop-ups. It's too bad that internet exploring has become a two-hand task now. But I guess it's also a good thing though - it keeps me in shape for all the copying and pasting of a SEO campaign.