When you click the link to invite friends there will be a little link that says "filter Friends"
. If you click on it you will see your Lists you have created. When you select a list only those people will show up in the choose area. But, now there is a new option to the right of the box. See it over there? It says "Select All"!
Cool huh? If you click it, it will automatically select everyone on that list.
Then you can even click the filter friends list again and select a different list you have created and select all of them. You can then click the little x next to the lists name and be back to the main list that shows all of your friends and select any stragglers. Butthe entire time it leaves the people you have already selected, selected. So when you are ready you just click the invite button and walaall those people are invited and you only clicked a couple of buttons!