"Just a quick tidbit of info to pass along, although this is an odd Zune issue, and an even odder solution. I actually lost the ability to sign in to the Zune Marketplace and therefore couldn't get new music from my Zune Pass subscription. I uninstalled and reinstalled the Zune software a number of times but to no avail. Here's what I saw: when clicking the Sign In button on Zune, nothing happened. Literally...nothing. It was like the button had no code behind it."
Perhaps an obscure problem, but a good one to document anyway - the eventual solution was to clear out his Temporary Internet Files. IE7 makes this a bit better, topping out by default at 1024 MB, but that's still huge and not needed in our broadband world. I have mine set around 50 MB or so.