I've had my Retina Macbook Pro since Oct 2013. From time to time (maybe once every 2-3 weeks), I do find a problem with my internet connection. I move between my home office ( running an Apple TC from 2010 / 2011 ) and my remote office downtown regularly.
Sometimes, I open my screen and and attempt to open my browser. Many times at my office location ( running a Cradle modem/router), the connection shows full-bars but I can't get anywhere. Naturally I turn off / on the WiFi via the OS menu bar and it fixes itself.
On some other networks (one particularly at a client's location), I receive the Exclimation Mark WIFI symbol immediately. Sometimes a software "reboot" of wifi will also fix the issue. Other times, I have to change to another available SSID for it to actually connect without the Exclaimation.
What brought me here...
For the last 48 hours, my Internet at home has been botchy. Seems like packet loss... my Internet Radio (di.fm / sky.fm) has been dropping after 20-30 seconds of streaming. In fact, I noticed that even pulling up small files ( < 1MB) from my TimeCapsule network drive was taking up to 30-45 seconds. Accessing my email from Mail has also been delayed and flagged errors connecting to my Gmail account. Finally after a day of intermittent access, I started to investigate more....
Long story short, stopping and starting my WiFi (from the OS menu bar) fixed the slowness immediately. Searching "2013 retina macbook wifi issues" brought me here and I have been reading the history. I have not gone through any drive swaps at this point, but simply wanted to back up the fact that on the most recent version of Mavericks on a 2013 rMBP, the WiFi seems to have hardward-based communication issues from time to time that will continue to happpen until a reboot of the WiFi system is performed ( restart of OS or simply turn Off WiFi, turn back On from menu bar ).
[ Also note, other "older" Macbooks on this same network do NOT have issues, nor any of my iOS devices... nearly eliminating all of the various routers as the problem... seems to be communication / protcol with the rMBP WiFi hardware card or driver that causes slow pings / packet loss until restarted ].