Ianto: it's canon that he keeps a handwritten diary. If he'd keep an online one . . . morethanteaboy in elsegame.. Some favorites: the kid!crack event, explaining Lisa, OMG WE'RE GETTING MARRIED, dealing with Jack's death and Internet Practices for the Beginning Blogger. It's wildly AU, of course, but thus is the nature of roleplay.

1941!Jack would find blogging a bit pointless, though I can easily see him keeping a handwritten diary.

GreenJack would post a lot of pictures of his children and memes, and occasional rants about politics. He'd also have a Deviantart account for his drawings, and quite probably try out every new gadget that came along until he got bored.