Got my Raspberry Pi 3 today (on Pi day, no less).
Playing with WiFi, I was getting a lot of stuttering, pauses, slow-downs, whatever you might want to call it. Pings bounced around in the range of 300ms and 2000ms, and interactive ssh was annoying. iperf, surprisingly, was showing me good-enough numbers.
Poking through the iwconfig man page, my best guess was that power management was possibly related to the problem. Doing a
sudo iwconfig wlan0 power off
turned off the power management stuff, and not too surprisingly, the WiFi stopped misbehaving. There are surely more refined adjustments that could be made, but I’m not worried about power management at the moment, so it’s a solution for me for now.