Richard McIntyre has posted about his experiences in working the features the Lithium framework into one of his current applications, mostly because of its support for Doctrine and its heavily decoupled nature.
I have a legacy application which was originally written in straight PHP with a few classes that I have created for convenience, but this is old and I am wanting to get this into a modern web framework. [...] I wanted to update my site with better validations anyway so I will start with flash messages and then validations. For flash messages in lithium you will need the li3_flash_message plugin.
He works through the different parts of the framework setup he needed including a simple bootstrap file and configuring it to use the li_flash_message library. He shows how to use validation rules on submitted data to ensure things like email an link format validity as well as spit back a message for any that are incorrect.