I had a really negative experience and then a very positive experience getting my L1.
First the negative... I spent 6 hours at the preclearence area at the Toronto airport while every single one of the customs officers came up with new and creative ways of denying my entry. I had to speak to the supervisor in order to make any progress because they were hung up on the fact that the signature from my company on the application form was 35 days old and it can't be more than 30 days. I finally got to the point where they were going to let me through I just had to go and get my actual degree since they wouldn't take the photocopy I provided. I left the airport and came back 20 minutes later with the degree and they did a shift change and I had to start all over. Ultimately, I did not get in and missed my
flight.
Now the positive... I crossed at the Sarnia border about 1 week later and the officers there right from the outside booth to the inside of the office were amazingly polite, reasonable and respectful. They read my file that the other officers in Toronto wrote in their system, and then they appologized that "those guys were so difficult".
Needless to say, I wouldn't recommend crossing through the airport!