I just attended the NSA Trusted Computing conference last week. I won't go into the details of the TPC panel discussion and what-not. Suffice to say that, yes, the manufacturer can, if it wanted to, lock out an OS other than Windows (or whatever comes installed.)
If the manufacturer will not provide you with what's necessary to undo that and install another OS, then you buy from someone else. Period.
The benefits of the Trusted Platform far outweigh the negatives in the DRM-scare camp. To me, this is like people who buy Apple products and then bitch because they can't install anything they want. No shyt, Sherlock.
We will see more of this UEFI/TPC stuff coming down the pipe, and it needs to. It is virtually impossible to secure a system with software alone. There must be cohesion between the hardware and software. After all, trusted software is only as trust-worthy as the hardware on which it runs.
I saw and heard about stuff last week which is just out-right scary, and makes me eager to attend DefCon or a Black Hat.