I am using my Windows 7 to share content via DLNA to my Google-TV. Frequently it doesn't update what it is sharing. At first I thought it was a codec problem, but then the media appeared a couple days later. The client has an update, and it sees deletions immediately, but still frequently doesn't find new files. Usually rebooting seems to work, but not always.
Luke's answer on a different question suggested that running Windows Media Player may cause the update to happen quicker. I don't usually run it, and running it this time resulted in everything updating. So this may in fact work.