Watch out for imperial line types loaded into a metric drawing, and vice-versa. Also watch out for implied scale factors ie. model space in meters, paper space in millimeters (paper space is always millimeters or inches, regardless of model space units), and annotation scale named 1:1000 with actual values of 1:1.
I've seen some drawings where the user apparently didn't grasp the concept of scaling and unit differences, with paper space title blocks scaled 1000x to compensate for an actual viewport scale of 1:1000.