The presence of WP7 Root Tools demonstrates this Lumia 800 is interop-unlocked
It has certainly been a very exciting 24 hours for Nokia fans between the early release of the 900 data-fix, that hilarous video from India or the prospect that "the Woz" may pick up a Lumia. And now we can add one more.
Over at XDA they have successfully figured out how to get the Lumia devices into unlocked bootloader mode (or rather, to detect if your phone has an unlocked bootloader). In turn, you can install a custom ROM with build 12070 (RM819_059P453_1600.2487.8107.12070_002) on board plus an interop-unlock.
The interop-unlock method goes deeper than developer unlocked on Mango phones but not as deep as a full-unlock. However, it will allow users to install some more sophisticated homebrew apps (e.g. registry editors) as opposed to just sideloading signed apps.
Unfortunately a lot of Lumia 800's won't have an unlocked bootloader (you'll need to check your phone first) but biktor_gj and the rest of the crew over at XDA will surely get to devices with newer firmware on board and unlock their bootloaders eventually.
At time of this writing, biktor_gj is still uploading the custom ROM for the Lumia 710 with interop unlock, though it should be up shortly and use the same process.
Certainly this is a big day for Lumia owners and just the tip of the iceberg for the custom ROMs to follow on these devices.