How do you add a grid on the viewer?

See if Safe Margins does what you want. You can turn that on/off through the flyout menu accessed from the upper left corner of the panel. In the Program Monitor, you can also get there via the Settings (wrench) button next to Duration. And if you want to toggle it on/off regularly, you can either add the button to the Monitor through Button Editor or assign a keyboard shortcut. Also, the Titler has both a Safe Title Margin and Safe Action Margin overlay.

some times I just add an custom Photshop img with guides as video layer... has no snapping function but you can completely customize it...

I do just as you outline. It's covered in my article on Alignment Grids: http://forums.adobe.com/message/4319250#4319250

I also agree that the Snap Tto Grid would be nice, like in Photoshop. I have sent in several Feature Requests for Grids, with full functions, like Snap To, though not recently.

Hunt

And do not forget that there are Alignment tools in the titler. So if you have one lined up on the grid, you can just align the other to the first one.