The implementation seems sloppy, completely unrestricted. They told us PvP servers would only merge with PvP, RP would only merge with RP, etc, but none of that is true, everything is mixed together. Also time zones are all mixed together, as you say, messing up anything that's supposed to start and end at a specific time, people missing their dailies and such. I also heard the cross realm stuff is contributing to an error I've been getting. (I thought it was my video card, kept trying new drivers.)
But even if the bugs were all fixed, I don't understand how cross realm helps the players. It means you see more people while leveling in out of the way areas, but they aren't people you can get to know and make a guild together. It erodes the sense of community, those servers that still seem to have a sense of community becomes as bad as all the others. They've already changed the leveling quests so you don't need to get groups together to complete them, so it seems odd to push to get more people in the environment now. It doesn't help the economy, which is what the low pop servers really needed. Also it's not restricted to low pop servers.
I think cross realm is here to stay. Blizzard wants it to manage system resources, just like phasing (another thing I dislike). So I hope they fix it so it's not a problem for players.
Why does sewage flow uphill leaving Undercity?