I have TrueCrypt with preboot authentication. Is it safe to make Windows auto-login?
There is no definite answer to this. It is just one extra line of defense you have. However if they can get past the encryption there is actually no reason why they wouldn't just mount the drive with some digital forensic tools (linux live disks) and extract the data from it.
I'm not sure if autologon also disables the possibility to lock your desktop. If it does I would leave it on. They can't copy your hard drive if you go to the toilet for 5 minutes, but they can sniff around if you leave it unlocked.