I've noticed that the banners especially (the most useless kind: every hour 'people are voting on your design' and 'a monster has appeared!') tend to cause a lot of lag. Not necessarily today, but in general. Cause I've been dealing with the issue of the game starting and then watching everything stop for a second, move again, stop, move etc. for months now. And it's always some banner, in-game mail or notification that appears as soon as the lag stops.
Which leads me to believe that its those things loading that's causing much of the lag. EA needs to seriously consider cutting these things from the game. I don't need notifications reminding me of the most basic stuff every hour and I don't care at all about the monster stuff. Just remove it or give us an option to play a basic version of the game, one that just has our own city, the design contest and some very basic assignments in the Mayor's pass (instead of all the complicated tasks and unnecessary shops that were only permanently added for them, that I'm not interested in anyway).
I don't mind so much that I can't play for a single day, but you guys do expect us to be online every day. Perhaps that isn't such a reasonable expectation, if you can't ensure that your game is actually playable. Either heavily trim it down, or just knock it off with the daily log in requirements, endless assignments and so on. You can't expect players to be online every day when your game isn't even capable of handling the traffic.