A breath of fresh air: Windows Mobile 6.1 for the Samsung Ace. Finally.
http://www.samsungmobileusa.com/i325/upgrade/
I'm blogging this from my laptop, tethered to my Ace. It's no long necessary to "unlock" the device, as they've set the security profile correctly to allow installation of apps. To tether a newly updated Ace:
Install and run a Registry editor.
Locate HKEY_LOCAL_MACHINE\Comm\InternetSharing and remove the value "InternetSharingEx.dll" from the key "Extension".
Reboot the phone.
Attach the Ace to your laptop.
On the Ace, go to Start and "Internet Sharing", and hit the Connect softkey. Your laptop should see a new NDIS device, and automatically connect to the Internet.