I quite like text resizing buttons on a page. As long as they're simple, obvious and work then I don't see a problem. Just another handy accessibility feature that less computer literate user may find useful. Presuming that all users who struggle to read average sized on screen text know how to use the accessibility features of their browser is a bit over presumptuous, in my opinion. Chnaging text size within the web page itself is often the most failsafe way of doing it, as long as it is done properly.

Pete.