GaAs technology still finds its extensive utilization in the desing and implementation of many high power consuming devices which requires low substrate losses such as Power Amplifiers in Wireless designs. Many of this technologies has its respective properties which finds its way into the industry of IC design with high realibility.
Even though GaAs will be the future technology.
Right now till 2015 CMOS will rule the semiconductor fabrication, since the process is well established.
In ultra submicron technology we have lot of issues in manufacturing, so semiconductor industries will opt for a stabilised fabrication process to avoid chip failure and heavy loss.
So it will take years to establish GaAs fabrication process as a commercial one, till that it will be a research field only.