I second this. If you don't know TeX math commands, there are toolbar buttons, menus, and dialog boxes for everything. But once you do learn the commands (and the TeX commands are listed in the menus and appear as tooltips over the buttons), you can just type them. So instead of pressing the subscript button, you press _ and the display switches to subscript mode. Instead of clicking the sine function, you type \sin. Instead of clicking the fraction button, you can type \frac.
Also, text entry is pretty easy. For example, after creating a fraction two empty blue squares appear--the numerator and the denomerator. Focus is in the numerator, and you can press Tab to switch to the denomerator. Pressing the spacebar exits the fraction, putting the cursor just after it.