I have a mid 2009(?) Macbook Pro running Mountain Lion. I'm not sure how relevant this is as I had this same issue on Snow Leopard. My issue is strange and I haven't been able to figure out what exactly is going on or where to ask.
I have a desktop at home running Windows 7 and no wireless capabilities. It does have bluetooth for whatever reason but I disabled it. What's weird is if I bring my laptop within ~3-4 feet of the desktop my wireless stops. But it doesn't stop as in, it goes away, I'm still technically connected to it I just don't get any information and I can't send any information, well sort of, I can still see other wireless access points. As soon as it's moved out of the area it turns right back on like nothing ever happened.
I haven't tested this with other computers as I don't know anyone who has a desktop that lives near me and I also never think to check with other people's laptops. Due to the nature of this problem it's hard to search for further information. My iPhone also seems to work fine around my computer but I'll test it at some point.
Any ideas what might be causing this?