I love the BL.
It has helped heeps in collecting articles. Anything that is marked with numbers and DSC is not onsite and takes a few days to be delivered (I think!). Also, it helps if you look on the catalogue to collect all the classmarks you want then either order them when you get there, or collect those slips to order any offsite stuff. Another issue is that you will be restricted on how many articles you place on order. Something like 10-12?! if you order stuff which is onsite; ie will be at the readers room reception in 90 mins, 2hrs, 4 hrs etc. You can order loads of stuff (without restriction) using reference request slips. It mayb an idea to visit Senate House as well if your collecting stuff. Senate House has open access to the majority of journals so you wont have to go through the process of ordering stuff. I hope this is of help to you.