Here is a transcript of my experience with ACER:
Sujith: Jeermy, Android 3.1 upgrade is already available.
Jeermy Alms: yes, but my unit is not upgrading
Sujith: Have you tried upgrading the system?
Jeermy Alms: yes, i have gone to settings -> about -> upgrade
Jeermy Alms: many times
Sujith: We provide upgrade through your carrier.
Jeermy Alms: the iconia tab a500 is not on a carier
Sujith: Please contact your carrier to upgrade the operating system.
Jeermy Alms: it is wifi only
Sujith: Did you check the updates?
Sujith: Please check the update manually to find Android 3.1.
Jeermy Alms: via settings, about, upgrade?
Sujith: It will be upgraded manually if you have checked in the updates.
Jeermy Alms: where
Sujith: When it is available for your tablet pc, your system will be upgraded automatically.
Jeermy Alms: yes, but how are they doing the roll out? When should I expect it?
Sujith: It will be provided by us according to the priority of the serial number of your tablet pc.