One different solution that seems to be working for my mid-2010 MBP so far is that I've turned off my connection to my iCloud account. I had a lot of connectivity problems over the last 3 months after upgrading to Mavericks and I have tried all other solutions posted (including, but not limited to, deleting preferences files, PRAM resets, SMC resets, reinstalling Mavericks, installing all updates, trying different browser/mail application combinations). These were usually (but not always) brought about when putting the machine to sleep. For the last two days, I've been intentionally "breaking" my wireless while leaving the console open (i.e. purposefully doing tasks that seemed correlated with the wireless going out -- putting it to sleep or tethering to my Phone over wireless). I kept getting two very consistent kinds of messages in the console when the wireless would drop. The first were related to power/access issues with the wireless card... for example, my status bar when clicking the wireless access would say that the wireless was on, when it wasn't -- and trying to power it up via networksetup at the Terminal would generally give me VendorID and secondary bus issues.
The rest of the messages that were appearing generally reported problems that typically are related to VPN (for example, issues with a utun0 interface) or to network processes that were not being resolved. However, I don't use a VPN, so I didn't know why that device was active. Then I found that Back to My Mac used a VPN connection, so piecing it together with some other console messages at the time that the wireless dropped, usually there was some com.apple.something process trying to access the network relating to something that I had linked in iCloud (sometimes it was Calendar, sometimes it was Mail, sometimes Safari) and often this would result in certain processes running through the en1 device being in a strange state according to netstat (FIN_WAIT_2) which would typically coincide with the wireless connection dying.
So finally, I took the following steps:
1. In System Preferences, log out from iCloud (note that it will delete any files stored locally from your machine -- but not from the Cloud obviously).
2. Shut down the machine and restart (note I specifically DID NOT try a PRAM reset -- a standard restart worked here).
Everything has worked perfectly since... I've tried putting the machine to sleep, tried powering up and down the wireless, tried using my usually super-problematic tetheringfrom my iPhone via wireless (this almost ALWAYS caused the wireless to end up in limbo and stop working). Things have been very stable and no strange console messages like what I was seeing before.
Conjecture (if anyone from Apple is monitoring this thread still and not just praying that Yosemite will solve the issue): There is some issue with the iCloud connection in Mavericks that is causing the wireless device to become partially (but not completely) disabled because they're not completely closing the connection. I would guess that there is some process that is not being exited properly when the wireless connectivity drops completely because of sleep (or weak wireless connectivity).
It would be good if anyone who has been using work arounds like deleting preferences files or using a dongle could try this simple solution to see if it also worked for them.
