So far, I have more or less caught up on every series that I read up to Identity Crisis. Plus, I have just finished rereading that, too.
I'm not sure exactly what I thought I'd find out by doing this. I really don't think that there's anything going on that hasn't already played out, though I guess you never know. But here are a couple of things that are significant in retrospect:
*At the end of the Crime Syndicate story arc in JLA, Batman ponders and mentions his interest in having a full-time surveillance system to watch over the Earth. Through the Crisis of Conscience arc in JLA, we realize that Batman will be / already is surveilling the JLA. This leads to Brother Eye and the OMACS.
*At the end of the first story arc in Superman / Batman, Lex Luthor, who has been injecting himself with venom, appears to be dead. He is, however, not, and comments at the end of the issue that "There will be a reckoning.. a CRISIS...". This segmemt was collected in the Prelude to Infinite Crisis compliation, but it came out over a year before that.
*At the end of the Supergirl arc in Superman / Batman, Superman gathers together all the heroes to introduce Supergirl to them, and says that they only all get together when there is a funeral and he wanted to have a happy occasion for them to gather. The next time they all gather is for Sue's funeral in Identity Crisis.
*Before Wargames starts in the Batman comics, Robin's father has discovered who he is and convinced him to quit. By the middle, Tim is back in the game, and is extremely concerned about his father's safety all throughout. For me, the saddest part of Identity Crisis was the death of Jack Drake. I know that Sue was supposed to be the big one, but the Elongated Man-period of JLA is not one that I'm overly familiar with and I don't have any particular attachment to him or to Sue. But I adore Tim. I think that the issue where his dad dies may be the most painful comic I have ever read.