I installed the update a few days ago and it worked...BUT only after doing the following:
1. open network preferences
2. hit the advanced button
3. under preferred networks
a. eliminate invalid networks (I had a few....like Apple Store)
b. select: remember network this computer has joined
c. save changes
I've been trying to find the solution to this for many hours and I found something that works for me on my 2009 21.5" iMac. We have a 2008 Macbook in the house also which is not having issues so I decided to check the settings against each other. In the network preference I unchecked the Ask to join new networks field. Viola! Working for me now with no issues.