I've not been, but I'm a little curious. Are there really that many people that go, and is it accessible by transit?
Take the subway to Union, walk one level up, follow the Harbourfront LRT signs & transfer onto the LRT, take the LRT one stop to Queens Quay, walk up the stairs, cross the street to where you see the Westin Harbour Castle and that is where the ferries depart to the Island. Lineup, buy a ticket and then wait for the Hanlan's Point ferry. When you arrive at Hanlan's Point follow the paved road south (the only way you can go), walk about 10-15 minutes past the Island Airport fence until you see a tennis court on your right. Head across the grass, find any path through the bushes that you can find and you'll be on the beach. You'll see signs advising that you are entering a clothing optional beach area. Stay south of the snow fence once on the beach, that's the clothing optional area... you'll figure that out once you get there. Enjoy a walk north of the fence to where the best beach is, but keep 'yer clothes on there!
On a sunny summer weekday your likely to find a couple hundred people enjoying the rays, weekends and holidays are considerably busier.
Have fun and remember to put extra sunscreen on those parts where the sun don't usually shine or you'll be sorry! If your shy, remember it is "clothing optional".
Notes: On weekends & holidays you MAY need a transfer to get onto the Harbourfront LRT, so to be safe, make sure you get one from your point of departure. Also, try to get to the ferry docks by noon Mon.- Fri. and by 11am on weekends to avoid long lineups to buy tickets. Don't go to the island on Caribanna week or when large concerts are being held because lineups are hours long.