So for the last few months, my wife has been having constant trouble with her MacBook, specifically, wireless connectivity. Our wireless network has always worked well for me, but hers was constantly un-responsive. Intenet connections would work for a minute or two, then hang. It was constantly trying to re-connect to the router. DNS names would not look up properly. Pings would never return. I tried upgrading from a DLink router to an Apple Internet Extreme ... same problem.
Was it a hardware issue? Suzy took her MacBook to the Apple Store. They noticed some oddities and tried re-installing the operating system (without wiping the drive).
Was it a Comcast issue? I mean, they are rat bastards and totally clueless ... and as it turns out, our cable connection was wired backwards and it was lucky we got any signal at all. But that never affected me, and even once Comcast came out and rewired it, the change didn't seem to make a difference for Suzy's MacBook.
Meanwhile, Samantha's Dell worked great on the wireless. So did Merlyn's MacBook Pro. And my MacBook Pro. And the Wii. It got so that every time Suzy would bring it up, I'd start getting angry because I couldn't fix it! And fixing things is what I do!
Last night, staring in frustration at her MacBook, I did something I should have done a ways back: launch Console.app and see if there was anything interesting in there. And there was ... endless error messages from "RealPlayer Downloader" (which was running in the dock) with messages specifically mentioning the network interfaces.
It wasn't clear what it was doing there. Calling home? Opening up ports? Suzy had installed RealPlayer to watch a work-related video for a client months past and had forgotten about it. Guess what? I removed the application (using AppZapper) and Suzy's internet connection has been smooth sailing ever since.
Moral of the story: Run, Run, Run away from RealPlayer!