DCS Service on HTC Desire Z
I asked htc what it is about and they responded with:


  The DCS Utility services and components are the programs on your
  telephone that allow connection to the internet provided by your
  mobile carrier. It stands for Data Connection Service.


A little vague. It also cannot be removed, they told me. And as the sense ui was constantly crashing I decided to install cyaogenmod. Best decision ever: not only is my data usage halved, the user interface is stable as a rock.