I came accross [MongoDB] a few months ago and it seemed like a perfect fit for many of the projects I am working. Extremely fast inserts, map-reduce for complex queries, and most importantly, scaling is a breeze.
Since I am a Zend Framework guy I created a simple base model class for MongoDB. It is a very simple wrapper, but is effective for what I need. I usually create model classes for each “Collection” just like I would create models for each table in MySQL. Each model class extends from the new MongoDB base class and allows a low level “active directory” type access to MongoDB documents.