[acoustix]

Finger speed will come with time for the most part. There are excercises you can do to help it along though.

Pick a fret on your high E string (we'll say the fifth fret)
Hold your index finger on that note
Strike the string once and hammer one half step up (the 6th fret) over and over as fast as you can with your middle finger until the sound dies out.
Then strike string again and hammer a whole step up (7th fret) with your ring finger over and over again until the sound dies.
Do it again on the the 8th fret with your pinky
Then repeat the same process on the B string, then your G, D....

Note that all the while you are holding the note on the 5th fret on each string.

This will improve speed, strength, and overall dexterity.