I have this problem: I normally have Bluetooth enabled so I can make use of my speaker system and Magic Trackpad on my mid-2012 11" MacBook Air (2.0 GHz i7, 8GB).
However, when it's enabled, Wi-Fi association does not complete well, either on boot or wake from sleep. In my case, the Wi-Fi icon in the menu bar oscillates a bit and generally gives up. Clicking the icon again may or may not show my network; if it does, I can click it and it will usually associate, though occasionally it complains that association failed. This happens on all networks I regularly use—one, a Buffalo AP, the other, a Linksys.
If I turn Bluetooth off, I can associate just as quickly as I ever have with no issues. I generally don't even see it trying to associate; it's done before I'm logged in.
This appears to be a Mavericks problem, as the folks in the linked Apple discussion are speculating. I know I never had it under ML. Unfortunately, I don't know exactly when I started having the issue, but it seems like it became prevalent around the time I bought the Magic Trackpad. This seems odd, though, since the Trackpad is tens of miles away on one of the networks I'm having issues with.
Is there a workaround that would allow me to leave Bluetooth enabled so I can much more easily use my Trackpad?