The Settings button lets you do a number of useful things for interacting with your desktop programs. When touch-screen controls and gestures are not enough, an Additional Keys button brings up just the important control keys from your keyboard (such as escape, directional arrows, shift, and control) instead of the whole keyboard. There's also a mouse pointer button that lets you left or right click on items and use the contextual menus just like you would on your desktop computer.
I tried Parallels Access with several different programs, and though it takes some getting used to with the touch-screen controls, all of them worked as they should. For all of you wondering whether you can launch games from your desktop computer, you can, but the slight delay and control limitations (you're not using a mouse, after all) make most games unplayable.
The only problem I encountered with Parallels Access was that it wasn't as responsive as using an actual desktop. This is certainly to be expected, but what it means is that you'll often have to try an action a couple of times to get it to work. Still, to get access to the programs on your desktop is probably worth the trouble.
Overall, Parallels Access is great for using programs from your desktop computer on your iPad. Though it's not quite as responsive as using the real thing, with a little patience, most actions can be completed as though you were using a desktop computer.