The problem with installing many applications from extra-devel and extra-testing is that any one of these applications could have caused the issue (if it is another application causing the problem) Do you have some sort of power saving application that might be messing with the Wifi (if you only have the issue with Wifi and not 3G)

The only other thing that I can suggest is to go through the apps that you have installed from the testing and dev repos and remove them one by one to see if this fixes the issue.