I generally leave my wifi on when I'm driving between work and home. When I leave the house and get to my office, I have to turn wifi off and back on to get my phone to join my office wifi network (and vice versa). Is there a setting somewhere when I can have it automatically jump on saved wifi networks?
It should automatically jump on if its saved. Make sure you have the wifi sleep turned off in the wifi settings.
I'm not set to sleep, and both my office and home networks are remembered. I'm on nightly 42.
If you're leaving Wi-fi on it should automatically connect when in range of those networks. If it doesn't you may want to try a full wipe of your device. Also, here is a really useful Tasker program for turning wifi on and off at certain destinations.
Wifi Automator - Tasker Wiki