I'm using a large Intuos 3 with Mac OSX 10.7.4 and LR4.1. Using the tablet does help with fine control when using brushes and gradients. I do find myself switching back and forth with the mouse when adjusting sliders in the Develop module, as I don't like the feel of trying to use the pen to make small slider adjustments.
Using a tablet with Photoshop is a huge advantage. With Lightroom it's nice, but for me it doesn't make as big a difference. Note that, in either case, knowing all the keyboard commands will greatly improve your efficiency - place the keyboard above the tablet, and use your left hand to change tools, brush sizes, hardness, etc., while your right hand uses the pen and tablet. (Or vice versa for left-hand-dominant persons.)