Is there a way to isolate an area of a mesh when Weight Painting? Is there a way of isolating a particular area of a model whilst Weight Painting? When in Weight Paint mode, and you can see your entire model in blue (0) is there any way of being able to focus on the part your working on without everything else obscuring your vision and potentially getting painted as well? 

Hiding parts of the model in Edit Mode has no effect in Weight Paint mode - they just reappear. I know you can paint areas within Edit Mode, but I'd like to do it in Weight Paint mode with my tablet.

If there is a way, how do you go about doing it?

It's quite frustrating when you've spent ages painting an area to get just right, you accidentally get paint on another part of the model, and then you spend ages trying to find out where and why a part of the armature is causing a strange mess up.

Hope this is informative enough.

Thanks
Using the button I have highlighted in the screenshot will basically translate what you see and have selected in edit mode, to weight paint mode.

So if I hid the top rim of the cup in edit mode, with that button enabled it's hidden in weight point mode.

You will need to have whatever faces you DO want to paint on selected however.