I have a MBA with osx 10.8.5 I had to use a workaround involving downgrading the IO80211family.kext file to the 10.8.4 version to fix a wireless issue I was having. Currently everything working fine so I have no immediate concerns. In my haste I forgot to back up the original file. I plan to upgrade to osx 10.9 when it comes out. I came across a few posts that said this workaround could potentially cause problems in the future when it comes to upgrades. If I upgraded to mavericks the normal way (via app store), could that potentially cause an issue? I'd think it would be fine, doesn't osx replace all the "system" files during a major upgrade? I'm not that knowledgable about OSX, so maybe I'm just being paranoid, but I was just wondering how exactly OSX upgrades work in regards to system files, and if I could potentially run into any issues.