The voice search on my droid works great, the voice dialer on the other hand is pathetic. I live in the midwest(known for having very clean english) and the damn thing can't even get "dial mom" correct.
I had the same problem, rarely did it get it right and always had to chose from a list. It never got my wifes name right EVER.
I downloaded Voice Dialer HF from DfxMobile and it nails it correct everytime, even from 20 feet away from my phone with ambient noise. PLUS it voice confirms your selectiona dn when you say "yes" it dials the number. Only one button tap to activate the app and from then on it is totally handsfree.
Cost $3.99 but well worth it. I know you will not be dissapointed!
Link to website for User Guide .. Voice Dialer HF (DFXmobile)
QR Code for app in Market