I did a search, and found several people having trunk opening problems - mostly related to the valet button inside the glove box. Well, my '08 has not such button, and the trunk release inside the car does work. So that rules out a fuse problem, no?
Anyone else have a similar issue? I don't want to take it in to the dealership...

 

Well i had the same issue and it may or may not be your issue, but the button on my remote went bad. So i had the remote replaced and that solved my issue. that might be a route you can attempt.

 

Wow - only the trunk release button was bad?
I have two remotes, and the trunk release doesn't work on either of them, but both fully function otherwise. That would be strange if that were the case...

 

The antenna in the trunk receiever could be bad. Mine is and needs replacement. Although the key button still works the button under near the license plate does not anymore. Take it to a dealership if under warranty and they should replace it free of charge. Have them check it out.

 

Yeah, that's the thing - it's not under warranty. Trying to avoid getting raped at the dealership if I can.

 

I would then look at a shop manual to track down what part it is so you can order it yourself and fix it. That's the only thing that's left. For a 06 and up models there is no valet in the glove compartment which is what I found out doing all the same searches you did and a poll so that rules it out. If both keys work with batteries in them and no warning on the dash for a low battery in the keys then it rules the keys out, and I doubt both are broken on the trunk switch. Only thing left is the receiver in the trunk.