I use voice dialing primarily to call my wife, let's call her "Helga". She's the only Helga in my contacts, so I could hold the button and say "call Helga mobile" and it would dial her iPhone.
Since I updated her phone to iOS5 (and enabled iCloud), when I say "call Helga mobile" my phone asks me which of four Helgas I wish to dial -- my wife or one of the three other Helgas in her contact list.
I've disable iCloud contact syncing on my phone but not yet on hers. If I go to http://www.icloud.com/, I can only use "Find my iPhone" there.
What else can I do?