xenForo is looking like a strong competitor from the start.
What is going to allow me (and many other webmasters) to change over would be a modification community and designers that can style the sites. It seems like there are lots of 'mods' that are already part of the script itself, so it will obviously reduce the need for a large modification community, but there needs to be one nonetheless.
Also, one of the major pieces of xenForo is going to be the integration of Facebook and Twitter features. Those will set xenForo apart and will allow for the social networking integration to continue to expand and mix with the forum sites.
Great work so far! :up: