Above is a quick video I put together recently to help all Gravity users set up their Twitter account with a predefined hash tag, and I can confirm today that the Official Nokia twitter hash tag for this years Nokia World 2010 in London, in indeed #NokiaWorld, so be sure to get yours set up today, or set up a search to follow all the Nokia World news next week.
In Gravity, as the video shows, you need to go into Search and Trends from your account screen, then hit options, and add a search, (Example #NokiaWorld), then once done, Gravity will collect all posts containing this hash tag.
Once Gravity has pulled in these results, go ahead, and select Options again, and scroll down to Settings.
Once in settings, if you have more than one twitter account set up, choose the twitter account you will be sending updates from that you wish for the auto hash tag to be added to every tweet.
Once selected, select save.
Now, its important to remember, in order for all your upcoming tweets that you wish to be auto tagged with your predefined hash tag, you must send your updates from the search and trends window by simply starting to type. These tweets will then automatically be predefined with your hash tag choice