Currently I'm in Berlin to attend the Magento U training. Even after having implemented some Magento shops this training is great and definetly inspiring to dig deeper into Magento code. Vinai does a great job showing in-depth insights on how the "Magento Framework" can be used and how it works behind the scenes.
Besides that he shows how to prevent pandas from dying by using the correct Magento techniques to solve common problems. (Too bad that there are too many developers out there who are not aware of the fact that those cute animals are dying whenever they do bad stuff like e.g. instanciating models with the "new" operator. For some kittens, koalas and baby dolphins this training came way too late.)