After working perfectly for the past 1.5 years I have had my 13" MBA, I suddenly had WIFI issues. Let me give a few details about my experience:
I suddenly had issues connecting to the internet (I was able to connect to the wifi, but could not load a webpage in less than 2-3 minutes if/when it loaded) at my home, but had no issues when connecting directly to my modem via an ethernet cable – thus, it was not a network card issue or an issue with my internet provider.
After that, I had suddenly begun having issues connecting to the networks at my office and school…which is when I began to get frustrated.
See my answer below for how I resolved this issue.
Best Answer
After having issues with my home, office, and school networks (i.e. all networks I tried connecting to), I realized that the only thing these networks all had in common (besides my computer) was that they were all secured networks.
When I tried connecting to an open network, I had no issues at all - thus my realization that some settings on my MBA got screwed up somehow, and the security authorization was screwing things up.
Resolution: To do a hard reset on your WIFI settings, go into Macintosh HD -> Library -> Preferences (see screenshot below). Remove the SystemConfiguration folder (place it on your Desktop for now). Reboot your MBA.
At this point, I had no issues connecting to any WIFI networks - I hope you have the same result.