Bug introduced in 10.0.0 or earlier and persisting through 10.0.1 and 10.0.2. Fixed in 10.1
It seems that the keyboard shortcuts for enlarging/reducing the font size (ALT+= / ALT+-) don't work anymore in M10 as it did in M9. If I select the text (or code) inside a cell they work. But if I select a cell or more cells they don't do anything anymore. The only way to change the font size of some cells is now to go through the Format-Size menu.
With M9 I used these shortcuts very often to gradually adjust the font size of one or more cells.
Maybe there is some setting in the Option Inspector that I must change? (I'm on windows 8.1 64bit)