some reason its not working for me :( I've upgraded from 3.7.5 to 3.8.1 and its not working :(

Most likely you are using a customised showthread template, therefore missing the template hook added in 3.8.0

How do i go about fixing it if so?

Just add:

$template_hook[showthread_after_activeusers]

after:

<!-- end currently active users -->
</if>

I manually did this myself after I noticed the same thing you did.

Thanks so much, it worked :)

Does this track views by un-registered guests?

i suggest to make new feature :

block in profile for every user and he has option to show his recent xx thread reading
and this is will be great feature for user profile if it will be depend on the who read thread hack from paul

All guests are unregistered ??

for the life of me I can't see it.. I have the hook in showthread already (I didn't have to edit)

There is nothing I can tell you without admin access to your forum.