I don't use the built in update functionality provided by the Update module for updating code. I like to use it for reminders and push back statistics of modules used for Drupal.org. However, someone people do use it. Sometimes this piece of functionality can fail and throw an interesting message which doesn't seem to have many answers despite the best Google-fu.
Drupal Commerce entities all make use of the "data" attribute. The data attribute is a blob that contain just about anything you would like - for example, Commerce Shipping utilizes this for shipping line items. Recently there was a StackExchange question on the documentation of this attribute.
If there's one thing we've all grown to encounter in Drupal it has, and probably will always be, configuration management. Drupal 8 is looking to solve a lot of that. However a lot of us don't live in the Drupal 8 world and can't sit and wait for that "magical" day. Features gives us a lot of functionality, but after a certain point Features either breaks down or becomes too cumbersome to manage.
One of the benefits to using Drupal is harnessing the command line tool Drush. If you don’t know about Drush, I advise heading over the the repository and also checking out this guide. Drush is powerful because its commands allow you to simplify your workflow - from clearing caches to migrating databases across environments. One of the best features, in my opinion, is the make command. Using Drush you can build Drupal with specific libraries and modules from a makefile. To make it even more awesome you can patch these projects through the makefile.
A recent project of mine has been ContribKanban.com for the Drupal community. The name speaks for itself - it provides a way for contributors to work on Drupal.org project issues queues through a kanban board. This app has two purposes: visualize the Drupal.org project issue queues in a useful fashion, and provide an experiment that tries to fully utilize Drupal.org APIs.