Things I've learned recently:

• Unity gain amplifiers (inverting and non-inverting) could be useful as simpler replacements for the more complex "simple" inverter and buffer that I've already built.
• You can get a High-Z output from an open collector by not using a pull-up resistor.
• Schmitt triggers are useful and easy to build.
• Analog is way more interesting than I thought.
• Application of positive and negative feedback in amplifier circuits can help you do some real sorcery.