I've read that pinging can leave a large footprint if you use the same IP address to ping all your backlinks at one go. It does sound somewhat ridiculous, but I if you ping Google or SEs directly, they can theoretically record your IP and know that it is only one person trying to get all those backlinks noticed, no? Does Google know this? Will they get the IP address of the person who pinged the link(s)? And what about 3rd party pinging services - Pingoat, Linklicious, etc? Paranoid much, but better to be safe than sorry. I usually ping everything directly to the SEs and never thought of this until now.