Cassiel

So, now that I have those Ortlieb backroller panniers everyone was so kind in pointing me to, what should I know about loading them? I used them yesterday to haul a ton of books back to the library and today to haul groceries, and they are truly da bomb. I am wondering, however, what I should know about handling the bike with heavy panniers or if there are effects I'm not aware of (what does it do to your tire life, for instance, to ride with a heavy load? Should I change the pressure in my tires since the load adds many pounds to my weight? How heavily can I load them without adverse effects?). Tips/tricks/traps?

yes

You may need or like more pressure in the back. You may need to weight the front of the bike more in hard corners. The bike may fall over while you are waiting for the elevator.

Cyclist0383

Put the heaver things on the rack side of the pannier, as low as possible in the bag. It'll help with handling a bit.

KnhoJ

You might notice the steering feels a bit strange with a rear load on the bike. Not a big deal, but if you get a bar bag or front basket a little weight up front fixes that.
Another one is handling the bike with weight on the back, when you're not on the bike. Like if you're holding just the bars, and lean it over just enough... The weight on the back will pivot towards the ground while the front tire goes up into the air! Usually only when people are watching, though.

gwd

Mine affect different bikes differently. My touring recumbent seems to handle better with the rear panniers loaded. I set the latches on the panniers to fit two different bikes so they aren't at the best position for either. On one of the bikes when I load it heavily a pannier will twist around the rack support an begin to touch the wheel. You might want to play with the latch settings to alter their position. For long trips, you might want your tools and rain gear packed on top. My Ortliebs are deep, so it is a pain to need a wrench or rain poncho stuck down in the bottom.

bragi

This one's obvious, but try to load the panniers evenly. I've sometimes had a lot of weight on one side but not the other, and that can get awkward if you stand up to go up a hill or something.

Also, you'll need to reconcile yourself to the fact that with panniers, you simply can't ride as aggressively. The balance is all messed up. Panniers are wonderfully practical for hauling stuff (IMO), but they transform your sporty bike into a minivan.