Seems to me that it's unlikely that you'd get hacked and have the hacker have the same interests and post unmalicious stuff on your favourite sites.

 Other possibilites?

1) Brain fade on your part, but not likely if you're sleep-posting stuff better than you do awake.  :)

2) NewAgTalk software has a memory leak or slight programming problem where it's losing track of the right IP to attach to msgs.  This seems to me to be qutie possibly if it's happened to other people, even if it's only rare.  I picked up 3/4 of a university degree in computer science before switching to farming so I know how something like this can happen and cause Ed and company to start pulling out their hair.

3) Seems to me that I can have myself logged onto NAT at multiple computers at the same time, so mebbe a like-minded friend of yours is at one of your other computers and didn't notice that the cookie logged him in automatically as you?  Other that or you were at a farming friend's place, took a few minutes to log in as you, check some mail, and then the next time he posted his computer logged him in as you.  Doesn't explain the IP address though, unless he's using your shared home network and NAT is logging the external IP of the modem and not the internal IP assigned to each specific computer inside the network.  That would have to be in conjunction with a MAC address though, cause otherwise there'd be a ton of msgs with 192.168.xxx.xxx as their IP address.