WOW. There is faulty reasoning used by a fundy who is denying another fundy's faulty belief.
[btw - Last Thursdayism, also called the Omphalos hypothesis, is the belief that for the world to be functional immediately upon creation, God created things like mountains, canyons, tree growth rings, fingernails, and other things that could indicate age of the earth, and since they were created that way they could not be used to determine the age of the earth, therefore the age of the earth cannot be determined by worldly means - a very fundy belief supported by some creationists]
"Last Thursdayism is false because I clearly remember events from before Last Thursday."
FAIL. That's not what Last Thursdayism is.
"It does not follow that God could have fixed our minds and experiences to make us think we only felt things before last Thursday."
Why not? Being omnipotent, it's certainly in God's power. Maybe He chose not to do so - ever though of that?
"For example I have a note with the date on it, "Wednesday, July 15, 2009." This would not be possible if the world was created on "Thursday July 16, 2009.""
Correct. Now let's apply this further. If you don't support Last Thursdayism, then you agree that the age of the earth CAN be determined by worldly means. And every dating method scientists have used indicates an Earth that is thousands of years old. Therefore young earth creationism is false as well.