The first presentation I attended was an excellent presentation about building distributed systems given by Udi Dahan. He talked a little about his open source enterprise service bus (ESB) nServiceBus. He had a boatload of material, and ran through it all - it was a little bit too much for the time, and yet he managed to do a good job of not crushing us with it all.
Some of the more interesting notes I took:
You might want to consider the security of the data in your local caches
Instead of just logging an exception and moving on, route messages that couldn't be processed to an error/exception queue, so that you can reprocess them later - you don't want to just drop that $5M order.
I'm paraphrasing here, but the thing Udi said that really hits home most for me: If you want to have control over anything, don't allow multiple applications to share a database
If you have the opportunity to see Udi speak, I highly recommend it. I'm hoping to get a chance to play around with nServiceBus - maybe I'll have somethign to write about that in the coming weeks.