The Dash in Ubuntu can be quite slow to launch. Sometimes, it takes a couple of seconds even on a fast machine. One way to make it faster is to turn off the Blur that it uses for beautifying its rendering of results.
To do this install the CompizConfig Settings Manager (CCSM) and open it. Go to Desktop > Ubuntu Unity Plugin > Experimental > Dash Blur and choose No Blur. The Dash should open a bit faster now.
Tried with: CompizConfig Settings Manager 0.9.5.92 and Ubuntu 12.04 LTS