Don't wear them and never thought to wear them as I wanted to be able to hear the noises around me. However, I may need to rethink this...
There is a limit to how much noise can be blocked by earplugs (somewhere in the 35-40 dB range). Sound is still transmitted through your body around the ear canal (primarily through the bones) so you still hear plenty of sound. Might be hard to make out specific words, but you are still going to hear cars, sirens, etc. It muffles a great deal of the wind noise in your helmet though.
I've been using ear plugs nearly as long as I've been riding. Foam plugs are cheap and convenient. But they should be replaced regularly, and you do have to be careful when rolling the foam plugs between your fingers before insertion. If it folds and creates a crease, the crease may remain after they expand and this can allow a great deal of high frequency noise at or near full volume.
I personally use the "World's Finest Ear Plug" brand of plugs. They are like clay and you just knead them and mold them into a taper. Insert them and crush the blunt end into the outer ear. They work really well. The only downsides are due to the clay-like properties. They pick up dirt easily and leave a residue on your fingers after kneading them. Over time, it can build up inside your gloves. They seal more consistently than foam plugs once you learn to put them in correctly.
I've been seeking a good set of ear buds recently. I have no desire to listen to music. But the speakers included with my SENA 20S aren't audible at speed. It really sucks to miss your exit because you can't hear your navigation directions. Perhaps my ear plugs are too good? haha. I'm trying out a 4th set now. Went through a pair of cheaper AKG buds that work pretty well when inserted correctly. But getting it to sit right is trying and despite being really low profile, it gets knocked out of place too easily (particularly when putting my helmet on).
Tried some Klipsch R6 buds. Very easy to get a great noise seal. But they stick out too far and get pulled out when putting my helmet on. Its a real shame as they sound great.
Decided to try a cheap set of Sony buds. Couldn't get those to seal in my ear canal at all.
Currently trying out a pair of Shure SE215's. They come with foam and silicone sleeves in three sizes each. The largest of each seal well and do a good job but gets dislodged kind of easily. I should be receiving a package of triple flange seals for it tonight. These should allow me to insert the sleeves deeper into my ear and hopefully that will hold them in place better while I put my helmet on. The only downside is the cable is really long (64"). I wish they made a shorter version as they can be detached at the buds.