As of January 2011, Hulu Plus, Hulu's subscription service, is still not available to Google TV. Hulu and Hulu's part owner, NBC Universal, are blocking Hulu from Google TV by detecting which version of Flash you're using. Your desktop computer's Web browser uses a different version of Flash than your phone or your Google TV.
However, that doesn't mean there aren't ways around the problem. PlayOn is subscription software that runs on a Windows PC and allows Hulu and other content to stream to Google TV, PlayStation 3, Wii, and other devices that support common streaming formats. It's not a pretty solution, and it's not a dedicated Hulu Plus app, but it is a difficult to block solution that you could use right now for around $40 per year. That's still cheaper than a Hulu Plus subscription.