We use the scikit-learn library for various machine-learning tasks at Zyte. For example, for text classification we'd typically build a statistical model using sklearn's Pipeline, FeatureUnion, some classifier (e.g. LinearSVC) + feature extraction and preprocessing classes.
We often have to write spiders that need to login to sites, in order to scrape data from them. Our customers provide us with the site, username and password, and we do the rest.