If you load multiple sites/keywords, it will just cycle through them. Sometimes its good, sometimes bad because you can just end up with ALL the links going to one site if that one get approved more than others.
It really depends why I am blasting. If it is my own personal website I am direct linking to, I will load every important page of my site to blast on.
If I am blasting web 2.0s, I just randomly load them all and blast away.
If I am trying to get something indexed, I will only blast that one page I am trying to get indexed.