Just took a quick look in the announce server logs, and
jb@announce2:/home/discosrv$ sudo tail v4/stats | grep Kept
1427047200 Kept:10057 Deleted:527 Took:0.0552s
That’s 10057 devices in the IPv4 cache when it does it’s hourly cleanout. Also, about 10% of those seem to have working IPv6 (assuming a negligible amount of IPv6-only devices).
jb@announce2:/home/discosrv$ sudo tail v6/stats | grep Kept
1427047200 Kept:1045 Deleted:46 Took:0.0106s
(There are most likely more users out there - this is just how many happen to have talked to the global discovery server during the last hour and a number that caught my eye. :)