As a follow-up question, do any of you have advice for biking with a high load (eg, groceries in a milk crate on rear rack)? I've never done so, and I'd like to avoid me2's fate.

Don't swing the bike back and forth. If you need to get out of the saddle try to move your body forward and bring you knees forward instead of to the sides. The motion is hard to describe but easy to figure out. Once you get used to the weight, you can realy zip though turns with the extra weight keeping the rear wheel firmly planted. (that statement is in need of a disclaimer: zipping through turns at a high rate of speed with a lot of weight over the rear wheel is inherently dangerous and can lead to a serious loss of skin, so do so at your own risk, and don't blame me if you crash )