The bins have grooves to keep them from sliding left and right. There is also a guard rail on the three sides of each shelf to keep the bins from falling off. Excellent use of shelving space, top shelf is unoccupied and can be used for large items. 
Pros: 
Easy to assemble
High capacity bins
Great finish
Cons:
Inconsitent fit (does not affect the structure)
No dividers included
No tilting out the bins if they are loaded

Bottom line: with this practicality of the unit I now want to try out the different bin configurations.