From the FAQ regarding Hubscores:
HubScore takes into account many factors and will change over time as data about its performance continues to stream in. It will also fluctuate quite a bit, seemingly at random, and that is nothing to worry about. The most important HubScore components that you should be concerned with include:
Amount of traffic - including percentage from reputable sources other than HubPages
The reputation of the Hubber - your Hubber Score and contribution to the community
The response of readers to your Hub - including comments, thumbs up, etc.
The uniqueness of content - copying content already available on the web will be highly penalized