I think we may have done this before, a couple years ago but I don't feel like sifting through the threads.
Throw out your experiences with each as well as what you think the defining differences are between these two types. I'm good friends with an SEI-Si and I'm trying to figure out if someone else I know is SLI-Si. So... any compare and contrast would be good. Or if you know just one or the other, that's good too.