The following is from http://hubpages.com/community/Hubscore#mod_903926...
HubScore takes into account a number of factors, and will vary quite a bit from the time a Hub is published as data about its performance continues to stream in. The most important HubScore components that you should be concerned with include:
Amount of traffic, including percentage from sources other than HubPages
The length of the Hub (the more unique writing, generally, the better)
The uniqueness of content (copying content already available on the Web will be penalized)
The number of thumbs-up votes from unique users
The overall quality of the Hubber (author HubScore and Status)
We reserve the right to change the factors used to assess a Hub’s HubScore as we continue to determine those that measure a great Hub.
The bottom line is if you write original, useful content, your HubScores will reflect the quality and work you've put into them.