Cadence, if you are applying just to your lawn, staying out of the drip line of your rhododendrons, you should be fine. I don't know of a formula to give you in measurement/feet, but staying outside the dripline (and you could always add a couple of feet to stay 'safe') would prevent lime over the root zone of your rhododendrons. Be careful if using a broadcast spreader for your lime that you don't overshoot your target grass :)

I don't lime grass every year, but the years I have applied lime I haven't had a problem with it affecting acid loving plants/rhododendrons in borders or beds.

It also depends on slope and drainage. Avoid areas above the rhododendrons where the lime can wash down.

Avoid using lime near rhododendrons in low spots. This normally isn't a problem since rhododendrons need good drainage and are normally not planted in low spots.

Great information, thanks. I've decided since I love my rhodies so much that I'm not going to lime my front lawn. I'll just add lime to the backyard where I have a lilac tree, butterfly bush and hydrangea. I don't think the lime will affect these.

Typical blue and pink hydrangeas tend to be pink when the soil is alkaline such as with lime. If the soil is acidic and aluminum is present, they tend to be blue. Unfortunately aluminum is toxic to rhododendrons and azaleas, so the aluminum sulfate that is used on hydrangeas to encourage hydrangeas to be blue will eventually kill rhododendrons and azaleas.

Here is a link that might be useful: How to grow rhododendrons and azaleas.