I've had problems with my Droid/F90, too.
One issue I found was using 86,,, as a contact for voice dial (the "," are pauses). I'd get an error screen saying "no number". Deleted the contact and it sync'd. The Droid has other means of dialing voice mail. No problems with this on my old Razr.
Other times, I'd just get a failure message. Restarting my F90 and/or deleting the Droid and re-pairing usually works.
Now, on my 2nd droid (the first returned for the #@&^ echo problem) I get all sorts of goofy contacts in my F90. Lots of , contacts with the box being first,last name holders. Weird.
[bTW, the new droid has the same echo problem. Sure hope the Dec 11 update fixes it or it is going back to Verizon permanently.]