An interesting development that sprang from a conversation I had with Sara Golemon at the Zend Conference last year: user-space PDO drivers. If you don't know what I'm talking about, it's the ability to be able to define classes in PHP that implement PDO drivers.
It'll be interesting to see what people make of this. I was chatting about it with Chris last night, and he suggested that it might serve as a useful bridge for systems that have no native library connectivity. PDO::User could be used to shoe-horn in connectivity without having to radically rewrite other application code. Another similar idea is to map older database extensions as PDO drivers.
It's still early days yet, but it will be interesting to see where this goes. Thanks Sara :)