Never seen it in a light aircraft but I've seen it literally hundreds of times doing the day (night) job. Most recent experience was near Hong Kong a couple of weeks ago, where the windscreen was covered in bright lines that looked like mini forked lightning. It was a fantastic light show that lasted for well over 10 minutes.
I've been hit by lightning six times and none of those involved St. Elmo's fire. Read into that what you will (but I have no problems flying in/with it).