This presentation by Rich Hickey, published at InfoQ, has so much to do with the things I am researching for Drools now and summarizes so well some of the important notions that we will have to deal with in the near future that I highly recommend it:
Are We There Yet?
"The future is a function from the past, it doesn't change it."
"Time is atomic, epochal succession of process events."
"There is no such thing as mutable objects. If you can really believe in that, you can build better systems."
If you want to understand the above quotes, watch the presentation. :)