ELB primer : A good place to start

If you are just starting off with ELB or even if you have worked with it for some time, here is a helpful blog post:

http://harish11g.blogspot.com/2012/07/aws-elastic-load-balancing-elb-amazon.html

I like these points in particular: 

Point 4) Amazon ELB is not designed for sudden load spikes /Flash traffic 

Note: Not for traffic that changes ever few seconds or even every few minutes.

Point 8) Amazon ELB cannot do Multi AWS Region Load Balancing

Note: Use Route53

Point 9) Amazon ELB sticks request when traffic is generated from Single IP

Note: I see this a lot in training classes as students are always hitting from same IP address.

Point 12) Amazon ELB can easily support more than 20K+ Concurrent reqs/sec

Note: In most cases, one ELB can support multiple systems.