I’ve been using the Zune software (which I have come to love) to manage my music since I started using Windows Phone 7.5.
Recently, I’ve had an issue searching the marketplace. After I hit enter for my search term, it just shows me the progress bar but never returns any results. I’ve searched for an answer before with no luck. Tried again today, and found this article which recommends changing your DNS entries to use OpenDNS instead of the default DNS from your ISP. It appears to have solved my problem. FYI, the OpenDNS IP addresses are here.
I suspect you could use Google’s DNS as well and see the issue resolved but I haven’t verified that.
It’s also important to be aware that there are some reasons against using public DNS servers. Weigh that vs solving your problem with Zune.