How about the voicemail quick dial icon (white symbol on bottom left of keypad under the * sign)?
On my Droid 1, I could tap that button and it'd dial *86 + my PIN + # and my VMs would start playing. On my Droid X, I have to either hold down the 1 button for quickdial or hit the notification area VM alert to have it dial my PIN. If I hit the VM icon in the lower left corner out of habit, I have to punch my PIN + # in manually.
Not a deal-breaker but very annoying ,especially when driving. My Droid 1 could do it, why can't my X? The VZW Pre Plus had this problem also, at least a few months ago when I last used one.