When Version 4.0 came out I tried it for the 'buzz' layer.
Buzz is a really cool tool and lots of people in the area/city including people from Google in Waterloo that use it. You can share text/pictures and in the future videos etc. in the future via GPS location.
The only problem with the Buzz layer is that they added twitter feeds about 3 days ago to the buzz list, and some people send 20-30-100 tweets per day and it hides the buzzes that are actually useful.
As for voice search (just installed) they use the 'phone button' to start the voice box, Im having problems with the iPAQ Data Messenger since this also starts the phone - and I would guess other device might have a problem using this key.