I often have customers peering over my shoulder while developing. I always count to ten in my head, before I hear the invertible request of 'can you increase your font size'.
So today I wrote a quick macro in Visual Studio 2008, to-do just that adding a couple of buttons onto the toolbar to give me a nice easy way of adjusting -

Here's the couple of little VBA macro's
Public Sub IncreaseFont()
DTE.Properties("FontsAndColors", "TextEditor").Item("FontSize").Value += 1
End Sub
Public Sub DecreaseFont()
DTE.Properties("FontsAndColors", "TextEditor").Item("FontSize").Value -= 1
End Sub